OK, let's work through this together. We're starting with 877 and we're going to multiply it by 100, which means we add 877 to itself 100 times.
Step 1: 0 + 877 = 877
Step 2: 877 + 877 = 1754
Step 3: 1754 + 877 = 2631
Step 4: 2631 + 877 = 3508
Step 5: 3508 + 877 = 4385
Step 6: 4385 + 877 = 5262
Step 7: 5262 + 877 = 6139
Step 8: 6139 + 877 = 7016
Step 9: 7016 + 877 = 7893
Step 10: 7893 + 877 = 8770
Step 11: 8770 + 877 = 9647
Step 12: 9647 + 877 = 10524
Step 13: 10524 + 877 = 11401
Step 14: 11401 + 877 = 12278
Step 15: 12278 + 877 = 13155
Step 16: 13155 + 877 = 14032
Step 17: 14032 + 877 = 14909
Step 18: 14909 + 877 = 15786
Step 19: 15786 + 877 = 16663
Step 20: 16663 + 877 = 17540
Step 21: 17540 + 877 = 18417
Step 22: 18417 + 877 = 19294
Step 23: 19294 + 877 = 20171
Step 24: 20171 + 877 = 21048
Step 25: 21048 + 877 = 21925
Step 26: 21925 + 877 = 22802
Step 27: 22802 + 877 = 23679
Step 28: 23679 + 877 = 24556
Step 29: 24556 + 877 = 25433
Step 30: 25433 + 877 = 26310
Step 31: 26310 + 877 = 27187
Step 32: 27187 + 877 = 28064
Step 33: 28064 + 877 = 28941
Step 34: 28941 + 877 = 29818
Step 35: 29818 + 877 = 30695
Step 36: 30695 + 877 = 31572
Step 37: 31572 + 877 = 32449
Step 38: 32449 + 877 = 33326
Step 39: 33326 + 877 = 34203
Step 40: 34203 + 877 = 35080
Step 41: 35080 + 877 = 35957
Step 42: 35957 + 877 = 36834
Step 43: 36834 + 877 = 37711
Step 44: 37711 + 877 = 38588
Step 45: 38588 + 877 = 39465
Step 46: 39465 + 877 = 40342
Step 47: 40342 + 877 = 41219
Step 48: 41219 + 877 = 42096
Step 49: 42096 + 877 = 42973
Step 50: 42973 + 877 = 43850
Step 51: 43850 + 877 = 44727
Step 52: 44727 + 877 = 45604
Step 53: 45604 + 877 = 46481
Step 54: 46481 + 877 = 47358
Step 55: 47358 + 877 = 48235
Step 56: 48235 + 877 = 49112
Step 57: 49112 + 877 = 49989
Step 58: 49989 + 877 = 50866
Step 59: 50866 + 877 = 51743
Step 60: 51743 + 877 = 52620
Step 61: 52620 + 877 = 53497
Step 62: 53497 + 877 = 54374
Step 63: 54374 + 877 = 55251
Step 64: 55251 + 877 = 56128
Step 65: 56128 + 877 = 57005
Step 66: 57005 + 877 = 57882
Step 67: 57882 + 877 = 58759
Step 68: 58759 + 877 = 59636
Step 69: 59636 + 877 = 60513
Step 70: 60513 + 877 = 61390
Step 71: 61390 + 877 = 62267
Step 72: 62267 + 877 = 63144
Step 73: 63144 + 877 = 64021
Step 74: 64021 + 877 = 64898
Step 75: 64898 + 877 = 65775
Step 76: 65775 + 877 = 66652
Step 77: 66652 + 877 = 67529
Step 78: 67529 + 877 = 68406
Step 79: 68406 + 877 = 69283
Step 80: 69283 + 877 = 70160
Step 81: 70160 + 877 = 71037
Step 82: 71037 + 877 = 71914
Step 83: 71914 + 877 = 72791
Step 84: 72791 + 877 = 73668
Step 85: 73668 + 877 = 74545
Step 86: 74545 + 877 = 75422
Step 87: 75422 + 877 = 76299
Step 88: 76299 + 877 = 77176
Step 89: 77176 + 877 = 78053
Step 90: 78053 + 877 = 78930
Step 91: 78930 + 877 = 79807
Step 92: 79807 + 877 = 80684
Step 93: 80684 + 877 = 81561
Step 94: 81561 + 877 = 82438
Step 95: 82438 + 877 = 83315
Step 96: 83315 + 877 = 84192
Step 97: 84192 + 877 = 85069
Step 98: 85069 + 877 = 85946
Step 99: 85946 + 877 = 86823
Step 100: 86823 + 877 = 87700

So, 877*100 = 87700