Let's roll up our sleeves and solve this. We have 555 and we're going to multiply it by 20, essentially adding 555 to itself 20 times.
Step 1: 0 + 555 = 555
Step 2: 555 + 555 = 1110
Step 3: 1110 + 555 = 1665
Step 4: 1665 + 555 = 2220
Step 5: 2220 + 555 = 2775
Step 6: 2775 + 555 = 3330
Step 7: 3330 + 555 = 3885
Step 8: 3885 + 555 = 4440
Step 9: 4440 + 555 = 4995
Step 10: 4995 + 555 = 5550
Step 11: 5550 + 555 = 6105
Step 12: 6105 + 555 = 6660
Step 13: 6660 + 555 = 7215
Step 14: 7215 + 555 = 7770
Step 15: 7770 + 555 = 8325
Step 16: 8325 + 555 = 8880
Step 17: 8880 + 555 = 9435
Step 18: 9435 + 555 = 9990
Step 19: 9990 + 555 = 10545
Step 20: 10545 + 555 = 11100

So, 555*20 = 11100