OK, let's crack this. We're given 841 and our task is to multiply it by 51. Essentially, we'll be adding 841 to itself 51 times.
Step 1: 0 + 841 = 841
Step 2: 841 + 841 = 1682
Step 3: 1682 + 841 = 2523
Step 4: 2523 + 841 = 3364
Step 5: 3364 + 841 = 4205
Step 6: 4205 + 841 = 5046
Step 7: 5046 + 841 = 5887
Step 8: 5887 + 841 = 6728
Step 9: 6728 + 841 = 7569
Step 10: 7569 + 841 = 8410
Step 11: 8410 + 841 = 9251
Step 12: 9251 + 841 = 10092
Step 13: 10092 + 841 = 10933
Step 14: 10933 + 841 = 11774
Step 15: 11774 + 841 = 12615
Step 16: 12615 + 841 = 13456
Step 17: 13456 + 841 = 14297
Step 18: 14297 + 841 = 15138
Step 19: 15138 + 841 = 15979
Step 20: 15979 + 841 = 16820
Step 21: 16820 + 841 = 17661
Step 22: 17661 + 841 = 18502
Step 23: 18502 + 841 = 19343
Step 24: 19343 + 841 = 20184
Step 25: 20184 + 841 = 21025
Step 26: 21025 + 841 = 21866
Step 27: 21866 + 841 = 22707
Step 28: 22707 + 841 = 23548
Step 29: 23548 + 841 = 24389
Step 30: 24389 + 841 = 25230
Step 31: 25230 + 841 = 26071
Step 32: 26071 + 841 = 26912
Step 33: 26912 + 841 = 27753
Step 34: 27753 + 841 = 28594
Step 35: 28594 + 841 = 29435
Step 36: 29435 + 841 = 30276
Step 37: 30276 + 841 = 31117
Step 38: 31117 + 841 = 31958
Step 39: 31958 + 841 = 32799
Step 40: 32799 + 841 = 33640
Step 41: 33640 + 841 = 34481
Step 42: 34481 + 841 = 35322
Step 43: 35322 + 841 = 36163
Step 44: 36163 + 841 = 37004
Step 45: 37004 + 841 = 37845
Step 46: 37845 + 841 = 38686
Step 47: 38686 + 841 = 39527
Step 48: 39527 + 841 = 40368
Step 49: 40368 + 841 = 41209
Step 50: 41209 + 841 = 42050
Step 51: 42050 + 841 = 42891

So, 841*51 = 42891