Let's roll up our sleeves and solve this. We have 825 and we're going to multiply it by 15, essentially adding 825 to itself 15 times.
Step 1: 0 + 825 = 825
Step 2: 825 + 825 = 1650
Step 3: 1650 + 825 = 2475
Step 4: 2475 + 825 = 3300
Step 5: 3300 + 825 = 4125
Step 6: 4125 + 825 = 4950
Step 7: 4950 + 825 = 5775
Step 8: 5775 + 825 = 6600
Step 9: 6600 + 825 = 7425
Step 10: 7425 + 825 = 8250
Step 11: 8250 + 825 = 9075
Step 12: 9075 + 825 = 9900
Step 13: 9900 + 825 = 10725
Step 14: 10725 + 825 = 11550
Step 15: 11550 + 825 = 12375

So, 825*15 = 12375