Let's roll up our sleeves and solve this. We have 623 and we're going to multiply it by 102, essentially adding 623 to itself 102 times.
Step 1: 0 + 623 = 623
Step 2: 623 + 623 = 1246
Step 3: 1246 + 623 = 1869
Step 4: 1869 + 623 = 2492
Step 5: 2492 + 623 = 3115
Step 6: 3115 + 623 = 3738
Step 7: 3738 + 623 = 4361
Step 8: 4361 + 623 = 4984
Step 9: 4984 + 623 = 5607
Step 10: 5607 + 623 = 6230
Step 11: 6230 + 623 = 6853
Step 12: 6853 + 623 = 7476
Step 13: 7476 + 623 = 8099
Step 14: 8099 + 623 = 8722
Step 15: 8722 + 623 = 9345
Step 16: 9345 + 623 = 9968
Step 17: 9968 + 623 = 10591
Step 18: 10591 + 623 = 11214
Step 19: 11214 + 623 = 11837
Step 20: 11837 + 623 = 12460
Step 21: 12460 + 623 = 13083
Step 22: 13083 + 623 = 13706
Step 23: 13706 + 623 = 14329
Step 24: 14329 + 623 = 14952
Step 25: 14952 + 623 = 15575
Step 26: 15575 + 623 = 16198
Step 27: 16198 + 623 = 16821
Step 28: 16821 + 623 = 17444
Step 29: 17444 + 623 = 18067
Step 30: 18067 + 623 = 18690
Step 31: 18690 + 623 = 19313
Step 32: 19313 + 623 = 19936
Step 33: 19936 + 623 = 20559
Step 34: 20559 + 623 = 21182
Step 35: 21182 + 623 = 21805
Step 36: 21805 + 623 = 22428
Step 37: 22428 + 623 = 23051
Step 38: 23051 + 623 = 23674
Step 39: 23674 + 623 = 24297
Step 40: 24297 + 623 = 24920
Step 41: 24920 + 623 = 25543
Step 42: 25543 + 623 = 26166
Step 43: 26166 + 623 = 26789
Step 44: 26789 + 623 = 27412
Step 45: 27412 + 623 = 28035
Step 46: 28035 + 623 = 28658
Step 47: 28658 + 623 = 29281
Step 48: 29281 + 623 = 29904
Step 49: 29904 + 623 = 30527
Step 50: 30527 + 623 = 31150
Step 51: 31150 + 623 = 31773
Step 52: 31773 + 623 = 32396
Step 53: 32396 + 623 = 33019
Step 54: 33019 + 623 = 33642
Step 55: 33642 + 623 = 34265
Step 56: 34265 + 623 = 34888
Step 57: 34888 + 623 = 35511
Step 58: 35511 + 623 = 36134
Step 59: 36134 + 623 = 36757
Step 60: 36757 + 623 = 37380
Step 61: 37380 + 623 = 38003
Step 62: 38003 + 623 = 38626
Step 63: 38626 + 623 = 39249
Step 64: 39249 + 623 = 39872
Step 65: 39872 + 623 = 40495
Step 66: 40495 + 623 = 41118
Step 67: 41118 + 623 = 41741
Step 68: 41741 + 623 = 42364
Step 69: 42364 + 623 = 42987
Step 70: 42987 + 623 = 43610
Step 71: 43610 + 623 = 44233
Step 72: 44233 + 623 = 44856
Step 73: 44856 + 623 = 45479
Step 74: 45479 + 623 = 46102
Step 75: 46102 + 623 = 46725
Step 76: 46725 + 623 = 47348
Step 77: 47348 + 623 = 47971
Step 78: 47971 + 623 = 48594
Step 79: 48594 + 623 = 49217
Step 80: 49217 + 623 = 49840
Step 81: 49840 + 623 = 50463
Step 82: 50463 + 623 = 51086
Step 83: 51086 + 623 = 51709
Step 84: 51709 + 623 = 52332
Step 85: 52332 + 623 = 52955
Step 86: 52955 + 623 = 53578
Step 87: 53578 + 623 = 54201
Step 88: 54201 + 623 = 54824
Step 89: 54824 + 623 = 55447
Step 90: 55447 + 623 = 56070
Step 91: 56070 + 623 = 56693
Step 92: 56693 + 623 = 57316
Step 93: 57316 + 623 = 57939
Step 94: 57939 + 623 = 58562
Step 95: 58562 + 623 = 59185
Step 96: 59185 + 623 = 59808
Step 97: 59808 + 623 = 60431
Step 98: 60431 + 623 = 61054
Step 99: 61054 + 623 = 61677
Step 100: 61677 + 623 = 62300
Step 101: 62300 + 623 = 62923
Step 102: 62923 + 623 = 63546

So, 623*102 = 63546