Let's roll up our sleeves and solve this. We have 505 and we're going to multiply it by 15, essentially adding 505 to itself 15 times.
Step 1: 0 + 505 = 505
Step 2: 505 + 505 = 1010
Step 3: 1010 + 505 = 1515
Step 4: 1515 + 505 = 2020
Step 5: 2020 + 505 = 2525
Step 6: 2525 + 505 = 3030
Step 7: 3030 + 505 = 3535
Step 8: 3535 + 505 = 4040
Step 9: 4040 + 505 = 4545
Step 10: 4545 + 505 = 5050
Step 11: 5050 + 505 = 5555
Step 12: 5555 + 505 = 6060
Step 13: 6060 + 505 = 6565
Step 14: 6565 + 505 = 7070
Step 15: 7070 + 505 = 7575

So, 505*15 = 7575