Let's roll up our sleeves and solve this. We have 503 and we're going to multiply it by 12, essentially adding 503 to itself 12 times.
Step 1: 0 + 503 = 503
Step 2: 503 + 503 = 1006
Step 3: 1006 + 503 = 1509
Step 4: 1509 + 503 = 2012
Step 5: 2012 + 503 = 2515
Step 6: 2515 + 503 = 3018
Step 7: 3018 + 503 = 3521
Step 8: 3521 + 503 = 4024
Step 9: 4024 + 503 = 4527
Step 10: 4527 + 503 = 5030
Step 11: 5030 + 503 = 5533
Step 12: 5533 + 503 = 6036

So, 503*12 = 6036