OK, let's work through this together. We're starting with 356 and we're going to multiply it by 420, which means we add 356 to itself 420 times.
Step 1: 0 + 356 = 356
Step 2: 356 + 356 = 712
Step 3: 712 + 356 = 1068
Step 4: 1068 + 356 = 1424
Step 5: 1424 + 356 = 1780
Step 6: 1780 + 356 = 2136
Step 7: 2136 + 356 = 2492
Step 8: 2492 + 356 = 2848
Step 9: 2848 + 356 = 3204
Step 10: 3204 + 356 = 3560
Step 11: 3560 + 356 = 3916
Step 12: 3916 + 356 = 4272
Step 13: 4272 + 356 = 4628
Step 14: 4628 + 356 = 4984
Step 15: 4984 + 356 = 5340
Step 16: 5340 + 356 = 5696
Step 17: 5696 + 356 = 6052
Step 18: 6052 + 356 = 6408
Step 19: 6408 + 356 = 6764
Step 20: 6764 + 356 = 7120
Step 21: 7120 + 356 = 7476
Step 22: 7476 + 356 = 7832
Step 23: 7832 + 356 = 8188
Step 24: 8188 + 356 = 8544
Step 25: 8544 + 356 = 8900
Step 26: 8900 + 356 = 9256
Step 27: 9256 + 356 = 9612
Step 28: 9612 + 356 = 9968
Step 29: 9968 + 356 = 10324
Step 30: 10324 + 356 = 10680
Step 31: 10680 + 356 = 11036
Step 32: 11036 + 356 = 11392
Step 33: 11392 + 356 = 11748
Step 34: 11748 + 356 = 12104
Step 35: 12104 + 356 = 12460
Step 36: 12460 + 356 = 12816
Step 37: 12816 + 356 = 13172
Step 38: 13172 + 356 = 13528
Step 39: 13528 + 356 = 13884
Step 40: 13884 + 356 = 14240
Step 41: 14240 + 356 = 14596
Step 42: 14596 + 356 = 14952
Step 43: 14952 + 356 = 15308
Step 44: 15308 + 356 = 15664
Step 45: 15664 + 356 = 16020
Step 46: 16020 + 356 = 16376
Step 47: 16376 + 356 = 16732
Step 48: 16732 + 356 = 17088
Step 49: 17088 + 356 = 17444
Step 50: 17444 + 356 = 17800
Step 51: 17800 + 356 = 18156
Step 52: 18156 + 356 = 18512
Step 53: 18512 + 356 = 18868
Step 54: 18868 + 356 = 19224
Step 55: 19224 + 356 = 19580
Step 56: 19580 + 356 = 19936
Step 57: 19936 + 356 = 20292
Step 58: 20292 + 356 = 20648
Step 59: 20648 + 356 = 21004
Step 60: 21004 + 356 = 21360
Step 61: 21360 + 356 = 21716
Step 62: 21716 + 356 = 22072
Step 63: 22072 + 356 = 22428
Step 64: 22428 + 356 = 22784
Step 65: 22784 + 356 = 23140
Step 66: 23140 + 356 = 23496
Step 67: 23496 + 356 = 23852
Step 68: 23852 + 356 = 24208
Step 69: 24208 + 356 = 24564
Step 70: 24564 + 356 = 24920
Step 71: 24920 + 356 = 25276
Step 72: 25276 + 356 = 25632
Step 73: 25632 + 356 = 25988
Step 74: 25988 + 356 = 26344
Step 75: 26344 + 356 = 26700
Step 76: 26700 + 356 = 27056
Step 77: 27056 + 356 = 27412
Step 78: 27412 + 356 = 27768
Step 79: 27768 + 356 = 28124
Step 80: 28124 + 356 = 28480
Step 81: 28480 + 356 = 28836
Step 82: 28836 + 356 = 29192
Step 83: 29192 + 356 = 29548
Step 84: 29548 + 356 = 29904
Step 85: 29904 + 356 = 30260
Step 86: 30260 + 356 = 30616
Step 87: 30616 + 356 = 30972
Step 88: 30972 + 356 = 31328
Step 89: 31328 + 356 = 31684
Step 90: 31684 + 356 = 32040
Step 91: 32040 + 356 = 32396
Step 92: 32396 + 356 = 32752
Step 93: 32752 + 356 = 33108
Step 94: 33108 + 356 = 33464
Step 95: 33464 + 356 = 33820
Step 96: 33820 + 356 = 34176
Step 97: 34176 + 356 = 34532
Step 98: 34532 + 356 = 34888
Step 99: 34888 + 356 = 35244
Step 100: 35244 + 356 = 35600
Step 101: 35600 + 356 = 35956
Step 102: 35956 + 356 = 36312
Step 103: 36312 + 356 = 36668
Step 104: 36668 + 356 = 37024
Step 105: 37024 + 356 = 37380
Step 106: 37380 + 356 = 37736
Step 107: 37736 + 356 = 38092
Step 108: 38092 + 356 = 38448
Step 109: 38448 + 356 = 38804
Step 110: 38804 + 356 = 39160
Step 111: 39160 + 356 = 39516
Step 112: 39516 + 356 = 39872
Step 113: 39872 + 356 = 40228
Step 114: 40228 + 356 = 40584
Step 115: 40584 + 356 = 40940
Step 116: 40940 + 356 = 41296
Step 117: 41296 + 356 = 41652
Step 118: 41652 + 356 = 42008
Step 119: 42008 + 356 = 42364
Step 120: 42364 + 356 = 42720
Step 121: 42720 + 356 = 43076
Step 122: 43076 + 356 = 43432
Step 123: 43432 + 356 = 43788
Step 124: 43788 + 356 = 44144
Step 125: 44144 + 356 = 44500
Step 126: 44500 + 356 = 44856
Step 127: 44856 + 356 = 45212
Step 128: 45212 + 356 = 45568
Step 129: 45568 + 356 = 45924
Step 130: 45924 + 356 = 46280
Step 131: 46280 + 356 = 46636
Step 132: 46636 + 356 = 46992
Step 133: 46992 + 356 = 47348
Step 134: 47348 + 356 = 47704
Step 135: 47704 + 356 = 48060
Step 136: 48060 + 356 = 48416
Step 137: 48416 + 356 = 48772
Step 138: 48772 + 356 = 49128
Step 139: 49128 + 356 = 49484
Step 140: 49484 + 356 = 49840
Step 141: 49840 + 356 = 50196
Step 142: 50196 + 356 = 50552
Step 143: 50552 + 356 = 50908
Step 144: 50908 + 356 = 51264
Step 145: 51264 + 356 = 51620
Step 146: 51620 + 356 = 51976
Step 147: 51976 + 356 = 52332
Step 148: 52332 + 356 = 52688
Step 149: 52688 + 356 = 53044
Step 150: 53044 + 356 = 53400
Step 151: 53400 + 356 = 53756
Step 152: 53756 + 356 = 54112
Step 153: 54112 + 356 = 54468
Step 154: 54468 + 356 = 54824
Step 155: 54824 + 356 = 55180
Step 156: 55180 + 356 = 55536
Step 157: 55536 + 356 = 55892
Step 158: 55892 + 356 = 56248
Step 159: 56248 + 356 = 56604
Step 160: 56604 + 356 = 56960
Step 161: 56960 + 356 = 57316
Step 162: 57316 + 356 = 57672
Step 163: 57672 + 356 = 58028
Step 164: 58028 + 356 = 58384
Step 165: 58384 + 356 = 58740
Step 166: 58740 + 356 = 59096
Step 167: 59096 + 356 = 59452
Step 168: 59452 + 356 = 59808
Step 169: 59808 + 356 = 60164
Step 170: 60164 + 356 = 60520
Step 171: 60520 + 356 = 60876
Step 172: 60876 + 356 = 61232
Step 173: 61232 + 356 = 61588
Step 174: 61588 + 356 = 61944
Step 175: 61944 + 356 = 62300
Step 176: 62300 + 356 = 62656
Step 177: 62656 + 356 = 63012
Step 178: 63012 + 356 = 63368
Step 179: 63368 + 356 = 63724
Step 180: 63724 + 356 = 64080
Step 181: 64080 + 356 = 64436
Step 182: 64436 + 356 = 64792
Step 183: 64792 + 356 = 65148
Step 184: 65148 + 356 = 65504
Step 185: 65504 + 356 = 65860
Step 186: 65860 + 356 = 66216
Step 187: 66216 + 356 = 66572
Step 188: 66572 + 356 = 66928
Step 189: 66928 + 356 = 67284
Step 190: 67284 + 356 = 67640
Step 191: 67640 + 356 = 67996
Step 192: 67996 + 356 = 68352
Step 193: 68352 + 356 = 68708
Step 194: 68708 + 356 = 69064
Step 195: 69064 + 356 = 69420
Step 196: 69420 + 356 = 69776
Step 197: 69776 + 356 = 70132
Step 198: 70132 + 356 = 70488
Step 199: 70488 + 356 = 70844
Step 200: 70844 + 356 = 71200
Step 201: 71200 + 356 = 71556
Step 202: 71556 + 356 = 71912
Step 203: 71912 + 356 = 72268
Step 204: 72268 + 356 = 72624
Step 205: 72624 + 356 = 72980
Step 206: 72980 + 356 = 73336
Step 207: 73336 + 356 = 73692
Step 208: 73692 + 356 = 74048
Step 209: 74048 + 356 = 74404
Step 210: 74404 + 356 = 74760
Step 211: 74760 + 356 = 75116
Step 212: 75116 + 356 = 75472
Step 213: 75472 + 356 = 75828
Step 214: 75828 + 356 = 76184
Step 215: 76184 + 356 = 76540
Step 216: 76540 + 356 = 76896
Step 217: 76896 + 356 = 77252
Step 218: 77252 + 356 = 77608
Step 219: 77608 + 356 = 77964
Step 220: 77964 + 356 = 78320
Step 221: 78320 + 356 = 78676
Step 222: 78676 + 356 = 79032
Step 223: 79032 + 356 = 79388
Step 224: 79388 + 356 = 79744
Step 225: 79744 + 356 = 80100
Step 226: 80100 + 356 = 80456
Step 227: 80456 + 356 = 80812
Step 228: 80812 + 356 = 81168
Step 229: 81168 + 356 = 81524
Step 230: 81524 + 356 = 81880
Step 231: 81880 + 356 = 82236
Step 232: 82236 + 356 = 82592
Step 233: 82592 + 356 = 82948
Step 234: 82948 + 356 = 83304
Step 235: 83304 + 356 = 83660
Step 236: 83660 + 356 = 84016
Step 237: 84016 + 356 = 84372
Step 238: 84372 + 356 = 84728
Step 239: 84728 + 356 = 85084
Step 240: 85084 + 356 = 85440
Step 241: 85440 + 356 = 85796
Step 242: 85796 + 356 = 86152
Step 243: 86152 + 356 = 86508
Step 244: 86508 + 356 = 86864
Step 245: 86864 + 356 = 87220
Step 246: 87220 + 356 = 87576
Step 247: 87576 + 356 = 87932
Step 248: 87932 + 356 = 88288
Step 249: 88288 + 356 = 88644
Step 250: 88644 + 356 = 89000
Step 251: 89000 + 356 = 89356
Step 252: 89356 + 356 = 89712
Step 253: 89712 + 356 = 90068
Step 254: 90068 + 356 = 90424
Step 255: 90424 + 356 = 90780
Step 256: 90780 + 356 = 91136
Step 257: 91136 + 356 = 91492
Step 258: 91492 + 356 = 91848
Step 259: 91848 + 356 = 92204
Step 260: 92204 + 356 = 92560
Step 261: 92560 + 356 = 92916
Step 262: 92916 + 356 = 93272
Step 263: 93272 + 356 = 93628
Step 264: 93628 + 356 = 93984
Step 265: 93984 + 356 = 94340
Step 266: 94340 + 356 = 94696
Step 267: 94696 + 356 = 95052
Step 268: 95052 + 356 = 95408
Step 269: 95408 + 356 = 95764
Step 270: 95764 + 356 = 96120
Step 271: 96120 + 356 = 96476
Step 272: 96476 + 356 = 96832
Step 273: 96832 + 356 = 97188
Step 274: 97188 + 356 = 97544
Step 275: 97544 + 356 = 97900
Step 276: 97900 + 356 = 98256
Step 277: 98256 + 356 = 98612
Step 278: 98612 + 356 = 98968
Step 279: 98968 + 356 = 99324
Step 280: 99324 + 356 = 99680
Step 281: 99680 + 356 = 100036
Step 282: 100036 + 356 = 100392
Step 283: 100392 + 356 = 100748
Step 284: 100748 + 356 = 101104
Step 285: 101104 + 356 = 101460
Step 286: 101460 + 356 = 101816
Step 287: 101816 + 356 = 102172
Step 288: 102172 + 356 = 102528
Step 289: 102528 + 356 = 102884
Step 290: 102884 + 356 = 103240
Step 291: 103240 + 356 = 103596
Step 292: 103596 + 356 = 103952
Step 293: 103952 + 356 = 104308
Step 294: 104308 + 356 = 104664
Step 295: 104664 + 356 = 105020
Step 296: 105020 + 356 = 105376
Step 297: 105376 + 356 = 105732
Step 298: 105732 + 356 = 106088
Step 299: 106088 + 356 = 106444
Step 300: 106444 + 356 = 106800
Step 301: 106800 + 356 = 107156
Step 302: 107156 + 356 = 107512
Step 303: 107512 + 356 = 107868
Step 304: 107868 + 356 = 108224
Step 305: 108224 + 356 = 108580
Step 306: 108580 + 356 = 108936
Step 307: 108936 + 356 = 109292
Step 308: 109292 + 356 = 109648
Step 309: 109648 + 356 = 110004
Step 310: 110004 + 356 = 110360
Step 311: 110360 + 356 = 110716
Step 312: 110716 + 356 = 111072
Step 313: 111072 + 356 = 111428
Step 314: 111428 + 356 = 111784
Step 315: 111784 + 356 = 112140
Step 316: 112140 + 356 = 112496
Step 317: 112496 + 356 = 112852
Step 318: 112852 + 356 = 113208
Step 319: 113208 + 356 = 113564
Step 320: 113564 + 356 = 113920
Step 321: 113920 + 356 = 114276
Step 322: 114276 + 356 = 114632
Step 323: 114632 + 356 = 114988
Step 324: 114988 + 356 = 115344
Step 325: 115344 + 356 = 115700
Step 326: 115700 + 356 = 116056
Step 327: 116056 + 356 = 116412
Step 328: 116412 + 356 = 116768
Step 329: 116768 + 356 = 117124
Step 330: 117124 + 356 = 117480
Step 331: 117480 + 356 = 117836
Step 332: 117836 + 356 = 118192
Step 333: 118192 + 356 = 118548
Step 334: 118548 + 356 = 118904
Step 335: 118904 + 356 = 119260
Step 336: 119260 + 356 = 119616
Step 337: 119616 + 356 = 119972
Step 338: 119972 + 356 = 120328
Step 339: 120328 + 356 = 120684
Step 340: 120684 + 356 = 121040
Step 341: 121040 + 356 = 121396
Step 342: 121396 + 356 = 121752
Step 343: 121752 + 356 = 122108
Step 344: 122108 + 356 = 122464
Step 345: 122464 + 356 = 122820
Step 346: 122820 + 356 = 123176
Step 347: 123176 + 356 = 123532
Step 348: 123532 + 356 = 123888
Step 349: 123888 + 356 = 124244
Step 350: 124244 + 356 = 124600
Step 351: 124600 + 356 = 124956
Step 352: 124956 + 356 = 125312
Step 353: 125312 + 356 = 125668
Step 354: 125668 + 356 = 126024
Step 355: 126024 + 356 = 126380
Step 356: 126380 + 356 = 126736
Step 357: 126736 + 356 = 127092
Step 358: 127092 + 356 = 127448
Step 359: 127448 + 356 = 127804
Step 360: 127804 + 356 = 128160
Step 361: 128160 + 356 = 128516
Step 362: 128516 + 356 = 128872
Step 363: 128872 + 356 = 129228
Step 364: 129228 + 356 = 129584
Step 365: 129584 + 356 = 129940
Step 366: 129940 + 356 = 130296
Step 367: 130296 + 356 = 130652
Step 368: 130652 + 356 = 131008
Step 369: 131008 + 356 = 131364
Step 370: 131364 + 356 = 131720
Step 371: 131720 + 356 = 132076
Step 372: 132076 + 356 = 132432
Step 373: 132432 + 356 = 132788
Step 374: 132788 + 356 = 133144
Step 375: 133144 + 356 = 133500
Step 376: 133500 + 356 = 133856
Step 377: 133856 + 356 = 134212
Step 378: 134212 + 356 = 134568
Step 379: 134568 + 356 = 134924
Step 380: 134924 + 356 = 135280
Step 381: 135280 + 356 = 135636
Step 382: 135636 + 356 = 135992
Step 383: 135992 + 356 = 136348
Step 384: 136348 + 356 = 136704
Step 385: 136704 + 356 = 137060
Step 386: 137060 + 356 = 137416
Step 387: 137416 + 356 = 137772
Step 388: 137772 + 356 = 138128
Step 389: 138128 + 356 = 138484
Step 390: 138484 + 356 = 138840
Step 391: 138840 + 356 = 139196
Step 392: 139196 + 356 = 139552
Step 393: 139552 + 356 = 139908
Step 394: 139908 + 356 = 140264
Step 395: 140264 + 356 = 140620
Step 396: 140620 + 356 = 140976
Step 397: 140976 + 356 = 141332
Step 398: 141332 + 356 = 141688
Step 399: 141688 + 356 = 142044
Step 400: 142044 + 356 = 142400
Step 401: 142400 + 356 = 142756
Step 402: 142756 + 356 = 143112
Step 403: 143112 + 356 = 143468
Step 404: 143468 + 356 = 143824
Step 405: 143824 + 356 = 144180
Step 406: 144180 + 356 = 144536
Step 407: 144536 + 356 = 144892
Step 408: 144892 + 356 = 145248
Step 409: 145248 + 356 = 145604
Step 410: 145604 + 356 = 145960
Step 411: 145960 + 356 = 146316
Step 412: 146316 + 356 = 146672
Step 413: 146672 + 356 = 147028
Step 414: 147028 + 356 = 147384
Step 415: 147384 + 356 = 147740
Step 416: 147740 + 356 = 148096
Step 417: 148096 + 356 = 148452
Step 418: 148452 + 356 = 148808
Step 419: 148808 + 356 = 149164
Step 420: 149164 + 356 = 149520

So, 356*420 = 149520