OK, let's work through this together. We're starting with 825 and we're going to multiply it by 20, which means we add 825 to itself 20 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
Step 16: 12375 + 825 = 13200
Step 17: 13200 + 825 = 14025
Step 18: 14025 + 825 = 14850
Step 19: 14850 + 825 = 15675
Step 20: 15675 + 825 = 16500

So, 825*20 = 16500