Let's roll up our sleeves and solve this. We have 811 and we're going to multiply it by 81, essentially adding 811 to itself 81 times.
Step 1: 0 + 811 = 811
Step 2: 811 + 811 = 1622
Step 3: 1622 + 811 = 2433
Step 4: 2433 + 811 = 3244
Step 5: 3244 + 811 = 4055
Step 6: 4055 + 811 = 4866
Step 7: 4866 + 811 = 5677
Step 8: 5677 + 811 = 6488
Step 9: 6488 + 811 = 7299
Step 10: 7299 + 811 = 8110
Step 11: 8110 + 811 = 8921
Step 12: 8921 + 811 = 9732
Step 13: 9732 + 811 = 10543
Step 14: 10543 + 811 = 11354
Step 15: 11354 + 811 = 12165
Step 16: 12165 + 811 = 12976
Step 17: 12976 + 811 = 13787
Step 18: 13787 + 811 = 14598
Step 19: 14598 + 811 = 15409
Step 20: 15409 + 811 = 16220
Step 21: 16220 + 811 = 17031
Step 22: 17031 + 811 = 17842
Step 23: 17842 + 811 = 18653
Step 24: 18653 + 811 = 19464
Step 25: 19464 + 811 = 20275
Step 26: 20275 + 811 = 21086
Step 27: 21086 + 811 = 21897
Step 28: 21897 + 811 = 22708
Step 29: 22708 + 811 = 23519
Step 30: 23519 + 811 = 24330
Step 31: 24330 + 811 = 25141
Step 32: 25141 + 811 = 25952
Step 33: 25952 + 811 = 26763
Step 34: 26763 + 811 = 27574
Step 35: 27574 + 811 = 28385
Step 36: 28385 + 811 = 29196
Step 37: 29196 + 811 = 30007
Step 38: 30007 + 811 = 30818
Step 39: 30818 + 811 = 31629
Step 40: 31629 + 811 = 32440
Step 41: 32440 + 811 = 33251
Step 42: 33251 + 811 = 34062
Step 43: 34062 + 811 = 34873
Step 44: 34873 + 811 = 35684
Step 45: 35684 + 811 = 36495
Step 46: 36495 + 811 = 37306
Step 47: 37306 + 811 = 38117
Step 48: 38117 + 811 = 38928
Step 49: 38928 + 811 = 39739
Step 50: 39739 + 811 = 40550
Step 51: 40550 + 811 = 41361
Step 52: 41361 + 811 = 42172
Step 53: 42172 + 811 = 42983
Step 54: 42983 + 811 = 43794
Step 55: 43794 + 811 = 44605
Step 56: 44605 + 811 = 45416
Step 57: 45416 + 811 = 46227
Step 58: 46227 + 811 = 47038
Step 59: 47038 + 811 = 47849
Step 60: 47849 + 811 = 48660
Step 61: 48660 + 811 = 49471
Step 62: 49471 + 811 = 50282
Step 63: 50282 + 811 = 51093
Step 64: 51093 + 811 = 51904
Step 65: 51904 + 811 = 52715
Step 66: 52715 + 811 = 53526
Step 67: 53526 + 811 = 54337
Step 68: 54337 + 811 = 55148
Step 69: 55148 + 811 = 55959
Step 70: 55959 + 811 = 56770
Step 71: 56770 + 811 = 57581
Step 72: 57581 + 811 = 58392
Step 73: 58392 + 811 = 59203
Step 74: 59203 + 811 = 60014
Step 75: 60014 + 811 = 60825
Step 76: 60825 + 811 = 61636
Step 77: 61636 + 811 = 62447
Step 78: 62447 + 811 = 63258
Step 79: 63258 + 811 = 64069
Step 80: 64069 + 811 = 64880
Step 81: 64880 + 811 = 65691

So, 811*81 = 65691