OK, let's crack this. We're given 51 and our task is to multiply it by 69. Essentially, we'll be adding 51 to itself 69 times.
Step 1: 0 + 51 = 51
Step 2: 51 + 51 = 102
Step 3: 102 + 51 = 153
Step 4: 153 + 51 = 204
Step 5: 204 + 51 = 255
Step 6: 255 + 51 = 306
Step 7: 306 + 51 = 357
Step 8: 357 + 51 = 408
Step 9: 408 + 51 = 459
Step 10: 459 + 51 = 510
Step 11: 510 + 51 = 561
Step 12: 561 + 51 = 612
Step 13: 612 + 51 = 663
Step 14: 663 + 51 = 714
Step 15: 714 + 51 = 765
Step 16: 765 + 51 = 816
Step 17: 816 + 51 = 867
Step 18: 867 + 51 = 918
Step 19: 918 + 51 = 969
Step 20: 969 + 51 = 1020
Step 21: 1020 + 51 = 1071
Step 22: 1071 + 51 = 1122
Step 23: 1122 + 51 = 1173
Step 24: 1173 + 51 = 1224
Step 25: 1224 + 51 = 1275
Step 26: 1275 + 51 = 1326
Step 27: 1326 + 51 = 1377
Step 28: 1377 + 51 = 1428
Step 29: 1428 + 51 = 1479
Step 30: 1479 + 51 = 1530
Step 31: 1530 + 51 = 1581
Step 32: 1581 + 51 = 1632
Step 33: 1632 + 51 = 1683
Step 34: 1683 + 51 = 1734
Step 35: 1734 + 51 = 1785
Step 36: 1785 + 51 = 1836
Step 37: 1836 + 51 = 1887
Step 38: 1887 + 51 = 1938
Step 39: 1938 + 51 = 1989
Step 40: 1989 + 51 = 2040
Step 41: 2040 + 51 = 2091
Step 42: 2091 + 51 = 2142
Step 43: 2142 + 51 = 2193
Step 44: 2193 + 51 = 2244
Step 45: 2244 + 51 = 2295
Step 46: 2295 + 51 = 2346
Step 47: 2346 + 51 = 2397
Step 48: 2397 + 51 = 2448
Step 49: 2448 + 51 = 2499
Step 50: 2499 + 51 = 2550
Step 51: 2550 + 51 = 2601
Step 52: 2601 + 51 = 2652
Step 53: 2652 + 51 = 2703
Step 54: 2703 + 51 = 2754
Step 55: 2754 + 51 = 2805
Step 56: 2805 + 51 = 2856
Step 57: 2856 + 51 = 2907
Step 58: 2907 + 51 = 2958
Step 59: 2958 + 51 = 3009
Step 60: 3009 + 51 = 3060
Step 61: 3060 + 51 = 3111
Step 62: 3111 + 51 = 3162
Step 63: 3162 + 51 = 3213
Step 64: 3213 + 51 = 3264
Step 65: 3264 + 51 = 3315
Step 66: 3315 + 51 = 3366
Step 67: 3366 + 51 = 3417
Step 68: 3417 + 51 = 3468
Step 69: 3468 + 51 = 3519

So, 51*69 = 3519