OK, let's crack this. We're given 729 and our task is to multiply it by 18. Essentially, we'll be adding 729 to itself 18 times.
Step 1: 0 + 729 = 729
Step 2: 729 + 729 = 1458
Step 3: 1458 + 729 = 2187
Step 4: 2187 + 729 = 2916
Step 5: 2916 + 729 = 3645
Step 6: 3645 + 729 = 4374
Step 7: 4374 + 729 = 5103
Step 8: 5103 + 729 = 5832
Step 9: 5832 + 729 = 6561
Step 10: 6561 + 729 = 7290
Step 11: 7290 + 729 = 8019
Step 12: 8019 + 729 = 8748
Step 13: 8748 + 729 = 9477
Step 14: 9477 + 729 = 10206
Step 15: 10206 + 729 = 10935
Step 16: 10935 + 729 = 11664
Step 17: 11664 + 729 = 12393
Step 18: 12393 + 729 = 13122

So, 729*18 = 13122