OK, let's work through this together. We're starting with 878 and we're going to multiply it by 121, which means we add 878 to itself 121 times.
Step 1: 0 + 878 = 878
Step 2: 878 + 878 = 1756
Step 3: 1756 + 878 = 2634
Step 4: 2634 + 878 = 3512
Step 5: 3512 + 878 = 4390
Step 6: 4390 + 878 = 5268
Step 7: 5268 + 878 = 6146
Step 8: 6146 + 878 = 7024
Step 9: 7024 + 878 = 7902
Step 10: 7902 + 878 = 8780
Step 11: 8780 + 878 = 9658
Step 12: 9658 + 878 = 10536
Step 13: 10536 + 878 = 11414
Step 14: 11414 + 878 = 12292
Step 15: 12292 + 878 = 13170
Step 16: 13170 + 878 = 14048
Step 17: 14048 + 878 = 14926
Step 18: 14926 + 878 = 15804
Step 19: 15804 + 878 = 16682
Step 20: 16682 + 878 = 17560
Step 21: 17560 + 878 = 18438
Step 22: 18438 + 878 = 19316
Step 23: 19316 + 878 = 20194
Step 24: 20194 + 878 = 21072
Step 25: 21072 + 878 = 21950
Step 26: 21950 + 878 = 22828
Step 27: 22828 + 878 = 23706
Step 28: 23706 + 878 = 24584
Step 29: 24584 + 878 = 25462
Step 30: 25462 + 878 = 26340
Step 31: 26340 + 878 = 27218
Step 32: 27218 + 878 = 28096
Step 33: 28096 + 878 = 28974
Step 34: 28974 + 878 = 29852
Step 35: 29852 + 878 = 30730
Step 36: 30730 + 878 = 31608
Step 37: 31608 + 878 = 32486
Step 38: 32486 + 878 = 33364
Step 39: 33364 + 878 = 34242
Step 40: 34242 + 878 = 35120
Step 41: 35120 + 878 = 35998
Step 42: 35998 + 878 = 36876
Step 43: 36876 + 878 = 37754
Step 44: 37754 + 878 = 38632
Step 45: 38632 + 878 = 39510
Step 46: 39510 + 878 = 40388
Step 47: 40388 + 878 = 41266
Step 48: 41266 + 878 = 42144
Step 49: 42144 + 878 = 43022
Step 50: 43022 + 878 = 43900
Step 51: 43900 + 878 = 44778
Step 52: 44778 + 878 = 45656
Step 53: 45656 + 878 = 46534
Step 54: 46534 + 878 = 47412
Step 55: 47412 + 878 = 48290
Step 56: 48290 + 878 = 49168
Step 57: 49168 + 878 = 50046
Step 58: 50046 + 878 = 50924
Step 59: 50924 + 878 = 51802
Step 60: 51802 + 878 = 52680
Step 61: 52680 + 878 = 53558
Step 62: 53558 + 878 = 54436
Step 63: 54436 + 878 = 55314
Step 64: 55314 + 878 = 56192
Step 65: 56192 + 878 = 57070
Step 66: 57070 + 878 = 57948
Step 67: 57948 + 878 = 58826
Step 68: 58826 + 878 = 59704
Step 69: 59704 + 878 = 60582
Step 70: 60582 + 878 = 61460
Step 71: 61460 + 878 = 62338
Step 72: 62338 + 878 = 63216
Step 73: 63216 + 878 = 64094
Step 74: 64094 + 878 = 64972
Step 75: 64972 + 878 = 65850
Step 76: 65850 + 878 = 66728
Step 77: 66728 + 878 = 67606
Step 78: 67606 + 878 = 68484
Step 79: 68484 + 878 = 69362
Step 80: 69362 + 878 = 70240
Step 81: 70240 + 878 = 71118
Step 82: 71118 + 878 = 71996
Step 83: 71996 + 878 = 72874
Step 84: 72874 + 878 = 73752
Step 85: 73752 + 878 = 74630
Step 86: 74630 + 878 = 75508
Step 87: 75508 + 878 = 76386
Step 88: 76386 + 878 = 77264
Step 89: 77264 + 878 = 78142
Step 90: 78142 + 878 = 79020
Step 91: 79020 + 878 = 79898
Step 92: 79898 + 878 = 80776
Step 93: 80776 + 878 = 81654
Step 94: 81654 + 878 = 82532
Step 95: 82532 + 878 = 83410
Step 96: 83410 + 878 = 84288
Step 97: 84288 + 878 = 85166
Step 98: 85166 + 878 = 86044
Step 99: 86044 + 878 = 86922
Step 100: 86922 + 878 = 87800
Step 101: 87800 + 878 = 88678
Step 102: 88678 + 878 = 89556
Step 103: 89556 + 878 = 90434
Step 104: 90434 + 878 = 91312
Step 105: 91312 + 878 = 92190
Step 106: 92190 + 878 = 93068
Step 107: 93068 + 878 = 93946
Step 108: 93946 + 878 = 94824
Step 109: 94824 + 878 = 95702
Step 110: 95702 + 878 = 96580
Step 111: 96580 + 878 = 97458
Step 112: 97458 + 878 = 98336
Step 113: 98336 + 878 = 99214
Step 114: 99214 + 878 = 100092
Step 115: 100092 + 878 = 100970
Step 116: 100970 + 878 = 101848
Step 117: 101848 + 878 = 102726
Step 118: 102726 + 878 = 103604
Step 119: 103604 + 878 = 104482
Step 120: 104482 + 878 = 105360
Step 121: 105360 + 878 = 106238

So, 878*121 = 106238