Let's roll up our sleeves and solve this. We have 900 and we're going to multiply it by 431, essentially adding 900 to itself 431 times.
Step 1: 0 + 900 = 900
Step 2: 900 + 900 = 1800
Step 3: 1800 + 900 = 2700
Step 4: 2700 + 900 = 3600
Step 5: 3600 + 900 = 4500
Step 6: 4500 + 900 = 5400
Step 7: 5400 + 900 = 6300
Step 8: 6300 + 900 = 7200
Step 9: 7200 + 900 = 8100
Step 10: 8100 + 900 = 9000
Step 11: 9000 + 900 = 9900
Step 12: 9900 + 900 = 10800
Step 13: 10800 + 900 = 11700
Step 14: 11700 + 900 = 12600
Step 15: 12600 + 900 = 13500
Step 16: 13500 + 900 = 14400
Step 17: 14400 + 900 = 15300
Step 18: 15300 + 900 = 16200
Step 19: 16200 + 900 = 17100
Step 20: 17100 + 900 = 18000
Step 21: 18000 + 900 = 18900
Step 22: 18900 + 900 = 19800
Step 23: 19800 + 900 = 20700
Step 24: 20700 + 900 = 21600
Step 25: 21600 + 900 = 22500
Step 26: 22500 + 900 = 23400
Step 27: 23400 + 900 = 24300
Step 28: 24300 + 900 = 25200
Step 29: 25200 + 900 = 26100
Step 30: 26100 + 900 = 27000
Step 31: 27000 + 900 = 27900
Step 32: 27900 + 900 = 28800
Step 33: 28800 + 900 = 29700
Step 34: 29700 + 900 = 30600
Step 35: 30600 + 900 = 31500
Step 36: 31500 + 900 = 32400
Step 37: 32400 + 900 = 33300
Step 38: 33300 + 900 = 34200
Step 39: 34200 + 900 = 35100
Step 40: 35100 + 900 = 36000
Step 41: 36000 + 900 = 36900
Step 42: 36900 + 900 = 37800
Step 43: 37800 + 900 = 38700
Step 44: 38700 + 900 = 39600
Step 45: 39600 + 900 = 40500
Step 46: 40500 + 900 = 41400
Step 47: 41400 + 900 = 42300
Step 48: 42300 + 900 = 43200
Step 49: 43200 + 900 = 44100
Step 50: 44100 + 900 = 45000
Step 51: 45000 + 900 = 45900
Step 52: 45900 + 900 = 46800
Step 53: 46800 + 900 = 47700
Step 54: 47700 + 900 = 48600
Step 55: 48600 + 900 = 49500
Step 56: 49500 + 900 = 50400
Step 57: 50400 + 900 = 51300
Step 58: 51300 + 900 = 52200
Step 59: 52200 + 900 = 53100
Step 60: 53100 + 900 = 54000
Step 61: 54000 + 900 = 54900
Step 62: 54900 + 900 = 55800
Step 63: 55800 + 900 = 56700
Step 64: 56700 + 900 = 57600
Step 65: 57600 + 900 = 58500
Step 66: 58500 + 900 = 59400
Step 67: 59400 + 900 = 60300
Step 68: 60300 + 900 = 61200
Step 69: 61200 + 900 = 62100
Step 70: 62100 + 900 = 63000
Step 71: 63000 + 900 = 63900
Step 72: 63900 + 900 = 64800
Step 73: 64800 + 900 = 65700
Step 74: 65700 + 900 = 66600
Step 75: 66600 + 900 = 67500
Step 76: 67500 + 900 = 68400
Step 77: 68400 + 900 = 69300
Step 78: 69300 + 900 = 70200
Step 79: 70200 + 900 = 71100
Step 80: 71100 + 900 = 72000
Step 81: 72000 + 900 = 72900
Step 82: 72900 + 900 = 73800
Step 83: 73800 + 900 = 74700
Step 84: 74700 + 900 = 75600
Step 85: 75600 + 900 = 76500
Step 86: 76500 + 900 = 77400
Step 87: 77400 + 900 = 78300
Step 88: 78300 + 900 = 79200
Step 89: 79200 + 900 = 80100
Step 90: 80100 + 900 = 81000
Step 91: 81000 + 900 = 81900
Step 92: 81900 + 900 = 82800
Step 93: 82800 + 900 = 83700
Step 94: 83700 + 900 = 84600
Step 95: 84600 + 900 = 85500
Step 96: 85500 + 900 = 86400
Step 97: 86400 + 900 = 87300
Step 98: 87300 + 900 = 88200
Step 99: 88200 + 900 = 89100
Step 100: 89100 + 900 = 90000
Step 101: 90000 + 900 = 90900
Step 102: 90900 + 900 = 91800
Step 103: 91800 + 900 = 92700
Step 104: 92700 + 900 = 93600
Step 105: 93600 + 900 = 94500
Step 106: 94500 + 900 = 95400
Step 107: 95400 + 900 = 96300
Step 108: 96300 + 900 = 97200
Step 109: 97200 + 900 = 98100
Step 110: 98100 + 900 = 99000
Step 111: 99000 + 900 = 99900
Step 112: 99900 + 900 = 100800
Step 113: 100800 + 900 = 101700
Step 114: 101700 + 900 = 102600
Step 115: 102600 + 900 = 103500
Step 116: 103500 + 900 = 104400
Step 117: 104400 + 900 = 105300
Step 118: 105300 + 900 = 106200
Step 119: 106200 + 900 = 107100
Step 120: 107100 + 900 = 108000
Step 121: 108000 + 900 = 108900
Step 122: 108900 + 900 = 109800
Step 123: 109800 + 900 = 110700
Step 124: 110700 + 900 = 111600
Step 125: 111600 + 900 = 112500
Step 126: 112500 + 900 = 113400
Step 127: 113400 + 900 = 114300
Step 128: 114300 + 900 = 115200
Step 129: 115200 + 900 = 116100
Step 130: 116100 + 900 = 117000
Step 131: 117000 + 900 = 117900
Step 132: 117900 + 900 = 118800
Step 133: 118800 + 900 = 119700
Step 134: 119700 + 900 = 120600
Step 135: 120600 + 900 = 121500
Step 136: 121500 + 900 = 122400
Step 137: 122400 + 900 = 123300
Step 138: 123300 + 900 = 124200
Step 139: 124200 + 900 = 125100
Step 140: 125100 + 900 = 126000
Step 141: 126000 + 900 = 126900
Step 142: 126900 + 900 = 127800
Step 143: 127800 + 900 = 128700
Step 144: 128700 + 900 = 129600
Step 145: 129600 + 900 = 130500
Step 146: 130500 + 900 = 131400
Step 147: 131400 + 900 = 132300
Step 148: 132300 + 900 = 133200
Step 149: 133200 + 900 = 134100
Step 150: 134100 + 900 = 135000
Step 151: 135000 + 900 = 135900
Step 152: 135900 + 900 = 136800
Step 153: 136800 + 900 = 137700
Step 154: 137700 + 900 = 138600
Step 155: 138600 + 900 = 139500
Step 156: 139500 + 900 = 140400
Step 157: 140400 + 900 = 141300
Step 158: 141300 + 900 = 142200
Step 159: 142200 + 900 = 143100
Step 160: 143100 + 900 = 144000
Step 161: 144000 + 900 = 144900
Step 162: 144900 + 900 = 145800
Step 163: 145800 + 900 = 146700
Step 164: 146700 + 900 = 147600
Step 165: 147600 + 900 = 148500
Step 166: 148500 + 900 = 149400
Step 167: 149400 + 900 = 150300
Step 168: 150300 + 900 = 151200
Step 169: 151200 + 900 = 152100
Step 170: 152100 + 900 = 153000
Step 171: 153000 + 900 = 153900
Step 172: 153900 + 900 = 154800
Step 173: 154800 + 900 = 155700
Step 174: 155700 + 900 = 156600
Step 175: 156600 + 900 = 157500
Step 176: 157500 + 900 = 158400
Step 177: 158400 + 900 = 159300
Step 178: 159300 + 900 = 160200
Step 179: 160200 + 900 = 161100
Step 180: 161100 + 900 = 162000
Step 181: 162000 + 900 = 162900
Step 182: 162900 + 900 = 163800
Step 183: 163800 + 900 = 164700
Step 184: 164700 + 900 = 165600
Step 185: 165600 + 900 = 166500
Step 186: 166500 + 900 = 167400
Step 187: 167400 + 900 = 168300
Step 188: 168300 + 900 = 169200
Step 189: 169200 + 900 = 170100
Step 190: 170100 + 900 = 171000
Step 191: 171000 + 900 = 171900
Step 192: 171900 + 900 = 172800
Step 193: 172800 + 900 = 173700
Step 194: 173700 + 900 = 174600
Step 195: 174600 + 900 = 175500
Step 196: 175500 + 900 = 176400
Step 197: 176400 + 900 = 177300
Step 198: 177300 + 900 = 178200
Step 199: 178200 + 900 = 179100
Step 200: 179100 + 900 = 180000
Step 201: 180000 + 900 = 180900
Step 202: 180900 + 900 = 181800
Step 203: 181800 + 900 = 182700
Step 204: 182700 + 900 = 183600
Step 205: 183600 + 900 = 184500
Step 206: 184500 + 900 = 185400
Step 207: 185400 + 900 = 186300
Step 208: 186300 + 900 = 187200
Step 209: 187200 + 900 = 188100
Step 210: 188100 + 900 = 189000
Step 211: 189000 + 900 = 189900
Step 212: 189900 + 900 = 190800
Step 213: 190800 + 900 = 191700
Step 214: 191700 + 900 = 192600
Step 215: 192600 + 900 = 193500
Step 216: 193500 + 900 = 194400
Step 217: 194400 + 900 = 195300
Step 218: 195300 + 900 = 196200
Step 219: 196200 + 900 = 197100
Step 220: 197100 + 900 = 198000
Step 221: 198000 + 900 = 198900
Step 222: 198900 + 900 = 199800
Step 223: 199800 + 900 = 200700
Step 224: 200700 + 900 = 201600
Step 225: 201600 + 900 = 202500
Step 226: 202500 + 900 = 203400
Step 227: 203400 + 900 = 204300
Step 228: 204300 + 900 = 205200
Step 229: 205200 + 900 = 206100
Step 230: 206100 + 900 = 207000
Step 231: 207000 + 900 = 207900
Step 232: 207900 + 900 = 208800
Step 233: 208800 + 900 = 209700
Step 234: 209700 + 900 = 210600
Step 235: 210600 + 900 = 211500
Step 236: 211500 + 900 = 212400
Step 237: 212400 + 900 = 213300
Step 238: 213300 + 900 = 214200
Step 239: 214200 + 900 = 215100
Step 240: 215100 + 900 = 216000
Step 241: 216000 + 900 = 216900
Step 242: 216900 + 900 = 217800
Step 243: 217800 + 900 = 218700
Step 244: 218700 + 900 = 219600
Step 245: 219600 + 900 = 220500
Step 246: 220500 + 900 = 221400
Step 247: 221400 + 900 = 222300
Step 248: 222300 + 900 = 223200
Step 249: 223200 + 900 = 224100
Step 250: 224100 + 900 = 225000
Step 251: 225000 + 900 = 225900
Step 252: 225900 + 900 = 226800
Step 253: 226800 + 900 = 227700
Step 254: 227700 + 900 = 228600
Step 255: 228600 + 900 = 229500
Step 256: 229500 + 900 = 230400
Step 257: 230400 + 900 = 231300
Step 258: 231300 + 900 = 232200
Step 259: 232200 + 900 = 233100
Step 260: 233100 + 900 = 234000
Step 261: 234000 + 900 = 234900
Step 262: 234900 + 900 = 235800
Step 263: 235800 + 900 = 236700
Step 264: 236700 + 900 = 237600
Step 265: 237600 + 900 = 238500
Step 266: 238500 + 900 = 239400
Step 267: 239400 + 900 = 240300
Step 268: 240300 + 900 = 241200
Step 269: 241200 + 900 = 242100
Step 270: 242100 + 900 = 243000
Step 271: 243000 + 900 = 243900
Step 272: 243900 + 900 = 244800
Step 273: 244800 + 900 = 245700
Step 274: 245700 + 900 = 246600
Step 275: 246600 + 900 = 247500
Step 276: 247500 + 900 = 248400
Step 277: 248400 + 900 = 249300
Step 278: 249300 + 900 = 250200
Step 279: 250200 + 900 = 251100
Step 280: 251100 + 900 = 252000
Step 281: 252000 + 900 = 252900
Step 282: 252900 + 900 = 253800
Step 283: 253800 + 900 = 254700
Step 284: 254700 + 900 = 255600
Step 285: 255600 + 900 = 256500
Step 286: 256500 + 900 = 257400
Step 287: 257400 + 900 = 258300
Step 288: 258300 + 900 = 259200
Step 289: 259200 + 900 = 260100
Step 290: 260100 + 900 = 261000
Step 291: 261000 + 900 = 261900
Step 292: 261900 + 900 = 262800
Step 293: 262800 + 900 = 263700
Step 294: 263700 + 900 = 264600
Step 295: 264600 + 900 = 265500
Step 296: 265500 + 900 = 266400
Step 297: 266400 + 900 = 267300
Step 298: 267300 + 900 = 268200
Step 299: 268200 + 900 = 269100
Step 300: 269100 + 900 = 270000
Step 301: 270000 + 900 = 270900
Step 302: 270900 + 900 = 271800
Step 303: 271800 + 900 = 272700
Step 304: 272700 + 900 = 273600
Step 305: 273600 + 900 = 274500
Step 306: 274500 + 900 = 275400
Step 307: 275400 + 900 = 276300
Step 308: 276300 + 900 = 277200
Step 309: 277200 + 900 = 278100
Step 310: 278100 + 900 = 279000
Step 311: 279000 + 900 = 279900
Step 312: 279900 + 900 = 280800
Step 313: 280800 + 900 = 281700
Step 314: 281700 + 900 = 282600
Step 315: 282600 + 900 = 283500
Step 316: 283500 + 900 = 284400
Step 317: 284400 + 900 = 285300
Step 318: 285300 + 900 = 286200
Step 319: 286200 + 900 = 287100
Step 320: 287100 + 900 = 288000
Step 321: 288000 + 900 = 288900
Step 322: 288900 + 900 = 289800
Step 323: 289800 + 900 = 290700
Step 324: 290700 + 900 = 291600
Step 325: 291600 + 900 = 292500
Step 326: 292500 + 900 = 293400
Step 327: 293400 + 900 = 294300
Step 328: 294300 + 900 = 295200
Step 329: 295200 + 900 = 296100
Step 330: 296100 + 900 = 297000
Step 331: 297000 + 900 = 297900
Step 332: 297900 + 900 = 298800
Step 333: 298800 + 900 = 299700
Step 334: 299700 + 900 = 300600
Step 335: 300600 + 900 = 301500
Step 336: 301500 + 900 = 302400
Step 337: 302400 + 900 = 303300
Step 338: 303300 + 900 = 304200
Step 339: 304200 + 900 = 305100
Step 340: 305100 + 900 = 306000
Step 341: 306000 + 900 = 306900
Step 342: 306900 + 900 = 307800
Step 343: 307800 + 900 = 308700
Step 344: 308700 + 900 = 309600
Step 345: 309600 + 900 = 310500
Step 346: 310500 + 900 = 311400
Step 347: 311400 + 900 = 312300
Step 348: 312300 + 900 = 313200
Step 349: 313200 + 900 = 314100
Step 350: 314100 + 900 = 315000
Step 351: 315000 + 900 = 315900
Step 352: 315900 + 900 = 316800
Step 353: 316800 + 900 = 317700
Step 354: 317700 + 900 = 318600
Step 355: 318600 + 900 = 319500
Step 356: 319500 + 900 = 320400
Step 357: 320400 + 900 = 321300
Step 358: 321300 + 900 = 322200
Step 359: 322200 + 900 = 323100
Step 360: 323100 + 900 = 324000
Step 361: 324000 + 900 = 324900
Step 362: 324900 + 900 = 325800
Step 363: 325800 + 900 = 326700
Step 364: 326700 + 900 = 327600
Step 365: 327600 + 900 = 328500
Step 366: 328500 + 900 = 329400
Step 367: 329400 + 900 = 330300
Step 368: 330300 + 900 = 331200
Step 369: 331200 + 900 = 332100
Step 370: 332100 + 900 = 333000
Step 371: 333000 + 900 = 333900
Step 372: 333900 + 900 = 334800
Step 373: 334800 + 900 = 335700
Step 374: 335700 + 900 = 336600
Step 375: 336600 + 900 = 337500
Step 376: 337500 + 900 = 338400
Step 377: 338400 + 900 = 339300
Step 378: 339300 + 900 = 340200
Step 379: 340200 + 900 = 341100
Step 380: 341100 + 900 = 342000
Step 381: 342000 + 900 = 342900
Step 382: 342900 + 900 = 343800
Step 383: 343800 + 900 = 344700
Step 384: 344700 + 900 = 345600
Step 385: 345600 + 900 = 346500
Step 386: 346500 + 900 = 347400
Step 387: 347400 + 900 = 348300
Step 388: 348300 + 900 = 349200
Step 389: 349200 + 900 = 350100
Step 390: 350100 + 900 = 351000
Step 391: 351000 + 900 = 351900
Step 392: 351900 + 900 = 352800
Step 393: 352800 + 900 = 353700
Step 394: 353700 + 900 = 354600
Step 395: 354600 + 900 = 355500
Step 396: 355500 + 900 = 356400
Step 397: 356400 + 900 = 357300
Step 398: 357300 + 900 = 358200
Step 399: 358200 + 900 = 359100
Step 400: 359100 + 900 = 360000
Step 401: 360000 + 900 = 360900
Step 402: 360900 + 900 = 361800
Step 403: 361800 + 900 = 362700
Step 404: 362700 + 900 = 363600
Step 405: 363600 + 900 = 364500
Step 406: 364500 + 900 = 365400
Step 407: 365400 + 900 = 366300
Step 408: 366300 + 900 = 367200
Step 409: 367200 + 900 = 368100
Step 410: 368100 + 900 = 369000
Step 411: 369000 + 900 = 369900
Step 412: 369900 + 900 = 370800
Step 413: 370800 + 900 = 371700
Step 414: 371700 + 900 = 372600
Step 415: 372600 + 900 = 373500
Step 416: 373500 + 900 = 374400
Step 417: 374400 + 900 = 375300
Step 418: 375300 + 900 = 376200
Step 419: 376200 + 900 = 377100
Step 420: 377100 + 900 = 378000
Step 421: 378000 + 900 = 378900
Step 422: 378900 + 900 = 379800
Step 423: 379800 + 900 = 380700
Step 424: 380700 + 900 = 381600
Step 425: 381600 + 900 = 382500
Step 426: 382500 + 900 = 383400
Step 427: 383400 + 900 = 384300
Step 428: 384300 + 900 = 385200
Step 429: 385200 + 900 = 386100
Step 430: 386100 + 900 = 387000
Step 431: 387000 + 900 = 387900

So, 900*431 = 387900