Alright, let's solve this math problem step by step. First, we have the number 21. Next, we see the multiplication sign, which means we need to multiply something. And what are we multiplying it by? We multiply it by 375. So, we're going to take the number 21 and add it to itself 375 times.
Step 1: 0 + 21 = 21
Step 2: 21 + 21 = 42
Step 3: 42 + 21 = 63
Step 4: 63 + 21 = 84
Step 5: 84 + 21 = 105
Step 6: 105 + 21 = 126
Step 7: 126 + 21 = 147
Step 8: 147 + 21 = 168
Step 9: 168 + 21 = 189
Step 10: 189 + 21 = 210
Step 11: 210 + 21 = 231
Step 12: 231 + 21 = 252
Step 13: 252 + 21 = 273
Step 14: 273 + 21 = 294
Step 15: 294 + 21 = 315
Step 16: 315 + 21 = 336
Step 17: 336 + 21 = 357
Step 18: 357 + 21 = 378
Step 19: 378 + 21 = 399
Step 20: 399 + 21 = 420
Step 21: 420 + 21 = 441
Step 22: 441 + 21 = 462
Step 23: 462 + 21 = 483
Step 24: 483 + 21 = 504
Step 25: 504 + 21 = 525
Step 26: 525 + 21 = 546
Step 27: 546 + 21 = 567
Step 28: 567 + 21 = 588
Step 29: 588 + 21 = 609
Step 30: 609 + 21 = 630
Step 31: 630 + 21 = 651
Step 32: 651 + 21 = 672
Step 33: 672 + 21 = 693
Step 34: 693 + 21 = 714
Step 35: 714 + 21 = 735
Step 36: 735 + 21 = 756
Step 37: 756 + 21 = 777
Step 38: 777 + 21 = 798
Step 39: 798 + 21 = 819
Step 40: 819 + 21 = 840
Step 41: 840 + 21 = 861
Step 42: 861 + 21 = 882
Step 43: 882 + 21 = 903
Step 44: 903 + 21 = 924
Step 45: 924 + 21 = 945
Step 46: 945 + 21 = 966
Step 47: 966 + 21 = 987
Step 48: 987 + 21 = 1008
Step 49: 1008 + 21 = 1029
Step 50: 1029 + 21 = 1050
Step 51: 1050 + 21 = 1071
Step 52: 1071 + 21 = 1092
Step 53: 1092 + 21 = 1113
Step 54: 1113 + 21 = 1134
Step 55: 1134 + 21 = 1155
Step 56: 1155 + 21 = 1176
Step 57: 1176 + 21 = 1197
Step 58: 1197 + 21 = 1218
Step 59: 1218 + 21 = 1239
Step 60: 1239 + 21 = 1260
Step 61: 1260 + 21 = 1281
Step 62: 1281 + 21 = 1302
Step 63: 1302 + 21 = 1323
Step 64: 1323 + 21 = 1344
Step 65: 1344 + 21 = 1365
Step 66: 1365 + 21 = 1386
Step 67: 1386 + 21 = 1407
Step 68: 1407 + 21 = 1428
Step 69: 1428 + 21 = 1449
Step 70: 1449 + 21 = 1470
Step 71: 1470 + 21 = 1491
Step 72: 1491 + 21 = 1512
Step 73: 1512 + 21 = 1533
Step 74: 1533 + 21 = 1554
Step 75: 1554 + 21 = 1575
Step 76: 1575 + 21 = 1596
Step 77: 1596 + 21 = 1617
Step 78: 1617 + 21 = 1638
Step 79: 1638 + 21 = 1659
Step 80: 1659 + 21 = 1680
Step 81: 1680 + 21 = 1701
Step 82: 1701 + 21 = 1722
Step 83: 1722 + 21 = 1743
Step 84: 1743 + 21 = 1764
Step 85: 1764 + 21 = 1785
Step 86: 1785 + 21 = 1806
Step 87: 1806 + 21 = 1827
Step 88: 1827 + 21 = 1848
Step 89: 1848 + 21 = 1869
Step 90: 1869 + 21 = 1890
Step 91: 1890 + 21 = 1911
Step 92: 1911 + 21 = 1932
Step 93: 1932 + 21 = 1953
Step 94: 1953 + 21 = 1974
Step 95: 1974 + 21 = 1995
Step 96: 1995 + 21 = 2016
Step 97: 2016 + 21 = 2037
Step 98: 2037 + 21 = 2058
Step 99: 2058 + 21 = 2079
Step 100: 2079 + 21 = 2100
Step 101: 2100 + 21 = 2121
Step 102: 2121 + 21 = 2142
Step 103: 2142 + 21 = 2163
Step 104: 2163 + 21 = 2184
Step 105: 2184 + 21 = 2205
Step 106: 2205 + 21 = 2226
Step 107: 2226 + 21 = 2247
Step 108: 2247 + 21 = 2268
Step 109: 2268 + 21 = 2289
Step 110: 2289 + 21 = 2310
Step 111: 2310 + 21 = 2331
Step 112: 2331 + 21 = 2352
Step 113: 2352 + 21 = 2373
Step 114: 2373 + 21 = 2394
Step 115: 2394 + 21 = 2415
Step 116: 2415 + 21 = 2436
Step 117: 2436 + 21 = 2457
Step 118: 2457 + 21 = 2478
Step 119: 2478 + 21 = 2499
Step 120: 2499 + 21 = 2520
Step 121: 2520 + 21 = 2541
Step 122: 2541 + 21 = 2562
Step 123: 2562 + 21 = 2583
Step 124: 2583 + 21 = 2604
Step 125: 2604 + 21 = 2625
Step 126: 2625 + 21 = 2646
Step 127: 2646 + 21 = 2667
Step 128: 2667 + 21 = 2688
Step 129: 2688 + 21 = 2709
Step 130: 2709 + 21 = 2730
Step 131: 2730 + 21 = 2751
Step 132: 2751 + 21 = 2772
Step 133: 2772 + 21 = 2793
Step 134: 2793 + 21 = 2814
Step 135: 2814 + 21 = 2835
Step 136: 2835 + 21 = 2856
Step 137: 2856 + 21 = 2877
Step 138: 2877 + 21 = 2898
Step 139: 2898 + 21 = 2919
Step 140: 2919 + 21 = 2940
Step 141: 2940 + 21 = 2961
Step 142: 2961 + 21 = 2982
Step 143: 2982 + 21 = 3003
Step 144: 3003 + 21 = 3024
Step 145: 3024 + 21 = 3045
Step 146: 3045 + 21 = 3066
Step 147: 3066 + 21 = 3087
Step 148: 3087 + 21 = 3108
Step 149: 3108 + 21 = 3129
Step 150: 3129 + 21 = 3150
Step 151: 3150 + 21 = 3171
Step 152: 3171 + 21 = 3192
Step 153: 3192 + 21 = 3213
Step 154: 3213 + 21 = 3234
Step 155: 3234 + 21 = 3255
Step 156: 3255 + 21 = 3276
Step 157: 3276 + 21 = 3297
Step 158: 3297 + 21 = 3318
Step 159: 3318 + 21 = 3339
Step 160: 3339 + 21 = 3360
Step 161: 3360 + 21 = 3381
Step 162: 3381 + 21 = 3402
Step 163: 3402 + 21 = 3423
Step 164: 3423 + 21 = 3444
Step 165: 3444 + 21 = 3465
Step 166: 3465 + 21 = 3486
Step 167: 3486 + 21 = 3507
Step 168: 3507 + 21 = 3528
Step 169: 3528 + 21 = 3549
Step 170: 3549 + 21 = 3570
Step 171: 3570 + 21 = 3591
Step 172: 3591 + 21 = 3612
Step 173: 3612 + 21 = 3633
Step 174: 3633 + 21 = 3654
Step 175: 3654 + 21 = 3675
Step 176: 3675 + 21 = 3696
Step 177: 3696 + 21 = 3717
Step 178: 3717 + 21 = 3738
Step 179: 3738 + 21 = 3759
Step 180: 3759 + 21 = 3780
Step 181: 3780 + 21 = 3801
Step 182: 3801 + 21 = 3822
Step 183: 3822 + 21 = 3843
Step 184: 3843 + 21 = 3864
Step 185: 3864 + 21 = 3885
Step 186: 3885 + 21 = 3906
Step 187: 3906 + 21 = 3927
Step 188: 3927 + 21 = 3948
Step 189: 3948 + 21 = 3969
Step 190: 3969 + 21 = 3990
Step 191: 3990 + 21 = 4011
Step 192: 4011 + 21 = 4032
Step 193: 4032 + 21 = 4053
Step 194: 4053 + 21 = 4074
Step 195: 4074 + 21 = 4095
Step 196: 4095 + 21 = 4116
Step 197: 4116 + 21 = 4137
Step 198: 4137 + 21 = 4158
Step 199: 4158 + 21 = 4179
Step 200: 4179 + 21 = 4200
Step 201: 4200 + 21 = 4221
Step 202: 4221 + 21 = 4242
Step 203: 4242 + 21 = 4263
Step 204: 4263 + 21 = 4284
Step 205: 4284 + 21 = 4305
Step 206: 4305 + 21 = 4326
Step 207: 4326 + 21 = 4347
Step 208: 4347 + 21 = 4368
Step 209: 4368 + 21 = 4389
Step 210: 4389 + 21 = 4410
Step 211: 4410 + 21 = 4431
Step 212: 4431 + 21 = 4452
Step 213: 4452 + 21 = 4473
Step 214: 4473 + 21 = 4494
Step 215: 4494 + 21 = 4515
Step 216: 4515 + 21 = 4536
Step 217: 4536 + 21 = 4557
Step 218: 4557 + 21 = 4578
Step 219: 4578 + 21 = 4599
Step 220: 4599 + 21 = 4620
Step 221: 4620 + 21 = 4641
Step 222: 4641 + 21 = 4662
Step 223: 4662 + 21 = 4683
Step 224: 4683 + 21 = 4704
Step 225: 4704 + 21 = 4725
Step 226: 4725 + 21 = 4746
Step 227: 4746 + 21 = 4767
Step 228: 4767 + 21 = 4788
Step 229: 4788 + 21 = 4809
Step 230: 4809 + 21 = 4830
Step 231: 4830 + 21 = 4851
Step 232: 4851 + 21 = 4872
Step 233: 4872 + 21 = 4893
Step 234: 4893 + 21 = 4914
Step 235: 4914 + 21 = 4935
Step 236: 4935 + 21 = 4956
Step 237: 4956 + 21 = 4977
Step 238: 4977 + 21 = 4998
Step 239: 4998 + 21 = 5019
Step 240: 5019 + 21 = 5040
Step 241: 5040 + 21 = 5061
Step 242: 5061 + 21 = 5082
Step 243: 5082 + 21 = 5103
Step 244: 5103 + 21 = 5124
Step 245: 5124 + 21 = 5145
Step 246: 5145 + 21 = 5166
Step 247: 5166 + 21 = 5187
Step 248: 5187 + 21 = 5208
Step 249: 5208 + 21 = 5229
Step 250: 5229 + 21 = 5250
Step 251: 5250 + 21 = 5271
Step 252: 5271 + 21 = 5292
Step 253: 5292 + 21 = 5313
Step 254: 5313 + 21 = 5334
Step 255: 5334 + 21 = 5355
Step 256: 5355 + 21 = 5376
Step 257: 5376 + 21 = 5397
Step 258: 5397 + 21 = 5418
Step 259: 5418 + 21 = 5439
Step 260: 5439 + 21 = 5460
Step 261: 5460 + 21 = 5481
Step 262: 5481 + 21 = 5502
Step 263: 5502 + 21 = 5523
Step 264: 5523 + 21 = 5544
Step 265: 5544 + 21 = 5565
Step 266: 5565 + 21 = 5586
Step 267: 5586 + 21 = 5607
Step 268: 5607 + 21 = 5628
Step 269: 5628 + 21 = 5649
Step 270: 5649 + 21 = 5670
Step 271: 5670 + 21 = 5691
Step 272: 5691 + 21 = 5712
Step 273: 5712 + 21 = 5733
Step 274: 5733 + 21 = 5754
Step 275: 5754 + 21 = 5775
Step 276: 5775 + 21 = 5796
Step 277: 5796 + 21 = 5817
Step 278: 5817 + 21 = 5838
Step 279: 5838 + 21 = 5859
Step 280: 5859 + 21 = 5880
Step 281: 5880 + 21 = 5901
Step 282: 5901 + 21 = 5922
Step 283: 5922 + 21 = 5943
Step 284: 5943 + 21 = 5964
Step 285: 5964 + 21 = 5985
Step 286: 5985 + 21 = 6006
Step 287: 6006 + 21 = 6027
Step 288: 6027 + 21 = 6048
Step 289: 6048 + 21 = 6069
Step 290: 6069 + 21 = 6090
Step 291: 6090 + 21 = 6111
Step 292: 6111 + 21 = 6132
Step 293: 6132 + 21 = 6153
Step 294: 6153 + 21 = 6174
Step 295: 6174 + 21 = 6195
Step 296: 6195 + 21 = 6216
Step 297: 6216 + 21 = 6237
Step 298: 6237 + 21 = 6258
Step 299: 6258 + 21 = 6279
Step 300: 6279 + 21 = 6300
Step 301: 6300 + 21 = 6321
Step 302: 6321 + 21 = 6342
Step 303: 6342 + 21 = 6363
Step 304: 6363 + 21 = 6384
Step 305: 6384 + 21 = 6405
Step 306: 6405 + 21 = 6426
Step 307: 6426 + 21 = 6447
Step 308: 6447 + 21 = 6468
Step 309: 6468 + 21 = 6489
Step 310: 6489 + 21 = 6510
Step 311: 6510 + 21 = 6531
Step 312: 6531 + 21 = 6552
Step 313: 6552 + 21 = 6573
Step 314: 6573 + 21 = 6594
Step 315: 6594 + 21 = 6615
Step 316: 6615 + 21 = 6636
Step 317: 6636 + 21 = 6657
Step 318: 6657 + 21 = 6678
Step 319: 6678 + 21 = 6699
Step 320: 6699 + 21 = 6720
Step 321: 6720 + 21 = 6741
Step 322: 6741 + 21 = 6762
Step 323: 6762 + 21 = 6783
Step 324: 6783 + 21 = 6804
Step 325: 6804 + 21 = 6825
Step 326: 6825 + 21 = 6846
Step 327: 6846 + 21 = 6867
Step 328: 6867 + 21 = 6888
Step 329: 6888 + 21 = 6909
Step 330: 6909 + 21 = 6930
Step 331: 6930 + 21 = 6951
Step 332: 6951 + 21 = 6972
Step 333: 6972 + 21 = 6993
Step 334: 6993 + 21 = 7014
Step 335: 7014 + 21 = 7035
Step 336: 7035 + 21 = 7056
Step 337: 7056 + 21 = 7077
Step 338: 7077 + 21 = 7098
Step 339: 7098 + 21 = 7119
Step 340: 7119 + 21 = 7140
Step 341: 7140 + 21 = 7161
Step 342: 7161 + 21 = 7182
Step 343: 7182 + 21 = 7203
Step 344: 7203 + 21 = 7224
Step 345: 7224 + 21 = 7245
Step 346: 7245 + 21 = 7266
Step 347: 7266 + 21 = 7287
Step 348: 7287 + 21 = 7308
Step 349: 7308 + 21 = 7329
Step 350: 7329 + 21 = 7350
Step 351: 7350 + 21 = 7371
Step 352: 7371 + 21 = 7392
Step 353: 7392 + 21 = 7413
Step 354: 7413 + 21 = 7434
Step 355: 7434 + 21 = 7455
Step 356: 7455 + 21 = 7476
Step 357: 7476 + 21 = 7497
Step 358: 7497 + 21 = 7518
Step 359: 7518 + 21 = 7539
Step 360: 7539 + 21 = 7560
Step 361: 7560 + 21 = 7581
Step 362: 7581 + 21 = 7602
Step 363: 7602 + 21 = 7623
Step 364: 7623 + 21 = 7644
Step 365: 7644 + 21 = 7665
Step 366: 7665 + 21 = 7686
Step 367: 7686 + 21 = 7707
Step 368: 7707 + 21 = 7728
Step 369: 7728 + 21 = 7749
Step 370: 7749 + 21 = 7770
Step 371: 7770 + 21 = 7791
Step 372: 7791 + 21 = 7812
Step 373: 7812 + 21 = 7833
Step 374: 7833 + 21 = 7854
Step 375: 7854 + 21 = 7875

So, 21*375 = 7875