OK, let's crack this. We're given 669 and our task is to multiply it by 75. Essentially, we'll be adding 669 to itself 75 times.
Step 1: 0 + 669 = 669
Step 2: 669 + 669 = 1338
Step 3: 1338 + 669 = 2007
Step 4: 2007 + 669 = 2676
Step 5: 2676 + 669 = 3345
Step 6: 3345 + 669 = 4014
Step 7: 4014 + 669 = 4683
Step 8: 4683 + 669 = 5352
Step 9: 5352 + 669 = 6021
Step 10: 6021 + 669 = 6690
Step 11: 6690 + 669 = 7359
Step 12: 7359 + 669 = 8028
Step 13: 8028 + 669 = 8697
Step 14: 8697 + 669 = 9366
Step 15: 9366 + 669 = 10035
Step 16: 10035 + 669 = 10704
Step 17: 10704 + 669 = 11373
Step 18: 11373 + 669 = 12042
Step 19: 12042 + 669 = 12711
Step 20: 12711 + 669 = 13380
Step 21: 13380 + 669 = 14049
Step 22: 14049 + 669 = 14718
Step 23: 14718 + 669 = 15387
Step 24: 15387 + 669 = 16056
Step 25: 16056 + 669 = 16725
Step 26: 16725 + 669 = 17394
Step 27: 17394 + 669 = 18063
Step 28: 18063 + 669 = 18732
Step 29: 18732 + 669 = 19401
Step 30: 19401 + 669 = 20070
Step 31: 20070 + 669 = 20739
Step 32: 20739 + 669 = 21408
Step 33: 21408 + 669 = 22077
Step 34: 22077 + 669 = 22746
Step 35: 22746 + 669 = 23415
Step 36: 23415 + 669 = 24084
Step 37: 24084 + 669 = 24753
Step 38: 24753 + 669 = 25422
Step 39: 25422 + 669 = 26091
Step 40: 26091 + 669 = 26760
Step 41: 26760 + 669 = 27429
Step 42: 27429 + 669 = 28098
Step 43: 28098 + 669 = 28767
Step 44: 28767 + 669 = 29436
Step 45: 29436 + 669 = 30105
Step 46: 30105 + 669 = 30774
Step 47: 30774 + 669 = 31443
Step 48: 31443 + 669 = 32112
Step 49: 32112 + 669 = 32781
Step 50: 32781 + 669 = 33450
Step 51: 33450 + 669 = 34119
Step 52: 34119 + 669 = 34788
Step 53: 34788 + 669 = 35457
Step 54: 35457 + 669 = 36126
Step 55: 36126 + 669 = 36795
Step 56: 36795 + 669 = 37464
Step 57: 37464 + 669 = 38133
Step 58: 38133 + 669 = 38802
Step 59: 38802 + 669 = 39471
Step 60: 39471 + 669 = 40140
Step 61: 40140 + 669 = 40809
Step 62: 40809 + 669 = 41478
Step 63: 41478 + 669 = 42147
Step 64: 42147 + 669 = 42816
Step 65: 42816 + 669 = 43485
Step 66: 43485 + 669 = 44154
Step 67: 44154 + 669 = 44823
Step 68: 44823 + 669 = 45492
Step 69: 45492 + 669 = 46161
Step 70: 46161 + 669 = 46830
Step 71: 46830 + 669 = 47499
Step 72: 47499 + 669 = 48168
Step 73: 48168 + 669 = 48837
Step 74: 48837 + 669 = 49506
Step 75: 49506 + 669 = 50175

So, 669*75 = 50175