OK, let's work through this together. We're starting with 793 and we're going to multiply it by 20, which means we add 793 to itself 20 times.
Step 1: 0 + 793 = 793
Step 2: 793 + 793 = 1586
Step 3: 1586 + 793 = 2379
Step 4: 2379 + 793 = 3172
Step 5: 3172 + 793 = 3965
Step 6: 3965 + 793 = 4758
Step 7: 4758 + 793 = 5551
Step 8: 5551 + 793 = 6344
Step 9: 6344 + 793 = 7137
Step 10: 7137 + 793 = 7930
Step 11: 7930 + 793 = 8723
Step 12: 8723 + 793 = 9516
Step 13: 9516 + 793 = 10309
Step 14: 10309 + 793 = 11102
Step 15: 11102 + 793 = 11895
Step 16: 11895 + 793 = 12688
Step 17: 12688 + 793 = 13481
Step 18: 13481 + 793 = 14274
Step 19: 14274 + 793 = 15067
Step 20: 15067 + 793 = 15860

So, 793*20 = 15860