Let's roll up our sleeves and solve this. We have 792 and we're going to multiply it by 20, essentially adding 792 to itself 20 times.
Step 1: 0 + 792 = 792
Step 2: 792 + 792 = 1584
Step 3: 1584 + 792 = 2376
Step 4: 2376 + 792 = 3168
Step 5: 3168 + 792 = 3960
Step 6: 3960 + 792 = 4752
Step 7: 4752 + 792 = 5544
Step 8: 5544 + 792 = 6336
Step 9: 6336 + 792 = 7128
Step 10: 7128 + 792 = 7920
Step 11: 7920 + 792 = 8712
Step 12: 8712 + 792 = 9504
Step 13: 9504 + 792 = 10296
Step 14: 10296 + 792 = 11088
Step 15: 11088 + 792 = 11880
Step 16: 11880 + 792 = 12672
Step 17: 12672 + 792 = 13464
Step 18: 13464 + 792 = 14256
Step 19: 14256 + 792 = 15048
Step 20: 15048 + 792 = 15840

So, 792*20 = 15840