Let's roll up our sleeves and solve this. We have 621 and we're going to multiply it by 108, essentially adding 621 to itself 108 times.
Step 1: 0 + 621 = 621
Step 2: 621 + 621 = 1242
Step 3: 1242 + 621 = 1863
Step 4: 1863 + 621 = 2484
Step 5: 2484 + 621 = 3105
Step 6: 3105 + 621 = 3726
Step 7: 3726 + 621 = 4347
Step 8: 4347 + 621 = 4968
Step 9: 4968 + 621 = 5589
Step 10: 5589 + 621 = 6210
Step 11: 6210 + 621 = 6831
Step 12: 6831 + 621 = 7452
Step 13: 7452 + 621 = 8073
Step 14: 8073 + 621 = 8694
Step 15: 8694 + 621 = 9315
Step 16: 9315 + 621 = 9936
Step 17: 9936 + 621 = 10557
Step 18: 10557 + 621 = 11178
Step 19: 11178 + 621 = 11799
Step 20: 11799 + 621 = 12420
Step 21: 12420 + 621 = 13041
Step 22: 13041 + 621 = 13662
Step 23: 13662 + 621 = 14283
Step 24: 14283 + 621 = 14904
Step 25: 14904 + 621 = 15525
Step 26: 15525 + 621 = 16146
Step 27: 16146 + 621 = 16767
Step 28: 16767 + 621 = 17388
Step 29: 17388 + 621 = 18009
Step 30: 18009 + 621 = 18630
Step 31: 18630 + 621 = 19251
Step 32: 19251 + 621 = 19872
Step 33: 19872 + 621 = 20493
Step 34: 20493 + 621 = 21114
Step 35: 21114 + 621 = 21735
Step 36: 21735 + 621 = 22356
Step 37: 22356 + 621 = 22977
Step 38: 22977 + 621 = 23598
Step 39: 23598 + 621 = 24219
Step 40: 24219 + 621 = 24840
Step 41: 24840 + 621 = 25461
Step 42: 25461 + 621 = 26082
Step 43: 26082 + 621 = 26703
Step 44: 26703 + 621 = 27324
Step 45: 27324 + 621 = 27945
Step 46: 27945 + 621 = 28566
Step 47: 28566 + 621 = 29187
Step 48: 29187 + 621 = 29808
Step 49: 29808 + 621 = 30429
Step 50: 30429 + 621 = 31050
Step 51: 31050 + 621 = 31671
Step 52: 31671 + 621 = 32292
Step 53: 32292 + 621 = 32913
Step 54: 32913 + 621 = 33534
Step 55: 33534 + 621 = 34155
Step 56: 34155 + 621 = 34776
Step 57: 34776 + 621 = 35397
Step 58: 35397 + 621 = 36018
Step 59: 36018 + 621 = 36639
Step 60: 36639 + 621 = 37260
Step 61: 37260 + 621 = 37881
Step 62: 37881 + 621 = 38502
Step 63: 38502 + 621 = 39123
Step 64: 39123 + 621 = 39744
Step 65: 39744 + 621 = 40365
Step 66: 40365 + 621 = 40986
Step 67: 40986 + 621 = 41607
Step 68: 41607 + 621 = 42228
Step 69: 42228 + 621 = 42849
Step 70: 42849 + 621 = 43470
Step 71: 43470 + 621 = 44091
Step 72: 44091 + 621 = 44712
Step 73: 44712 + 621 = 45333
Step 74: 45333 + 621 = 45954
Step 75: 45954 + 621 = 46575
Step 76: 46575 + 621 = 47196
Step 77: 47196 + 621 = 47817
Step 78: 47817 + 621 = 48438
Step 79: 48438 + 621 = 49059
Step 80: 49059 + 621 = 49680
Step 81: 49680 + 621 = 50301
Step 82: 50301 + 621 = 50922
Step 83: 50922 + 621 = 51543
Step 84: 51543 + 621 = 52164
Step 85: 52164 + 621 = 52785
Step 86: 52785 + 621 = 53406
Step 87: 53406 + 621 = 54027
Step 88: 54027 + 621 = 54648
Step 89: 54648 + 621 = 55269
Step 90: 55269 + 621 = 55890
Step 91: 55890 + 621 = 56511
Step 92: 56511 + 621 = 57132
Step 93: 57132 + 621 = 57753
Step 94: 57753 + 621 = 58374
Step 95: 58374 + 621 = 58995
Step 96: 58995 + 621 = 59616
Step 97: 59616 + 621 = 60237
Step 98: 60237 + 621 = 60858
Step 99: 60858 + 621 = 61479
Step 100: 61479 + 621 = 62100
Step 101: 62100 + 621 = 62721
Step 102: 62721 + 621 = 63342
Step 103: 63342 + 621 = 63963
Step 104: 63963 + 621 = 64584
Step 105: 64584 + 621 = 65205
Step 106: 65205 + 621 = 65826
Step 107: 65826 + 621 = 66447
Step 108: 66447 + 621 = 67068

So, 621*108 = 67068