Let's get this math done. We have 425 and we're going to multiply it by 21. This is the same as taking 425 and adding it to itself 21 times.
Step 1: 0 + 425 = 425
Step 2: 425 + 425 = 850
Step 3: 850 + 425 = 1275
Step 4: 1275 + 425 = 1700
Step 5: 1700 + 425 = 2125
Step 6: 2125 + 425 = 2550
Step 7: 2550 + 425 = 2975
Step 8: 2975 + 425 = 3400
Step 9: 3400 + 425 = 3825
Step 10: 3825 + 425 = 4250
Step 11: 4250 + 425 = 4675
Step 12: 4675 + 425 = 5100
Step 13: 5100 + 425 = 5525
Step 14: 5525 + 425 = 5950
Step 15: 5950 + 425 = 6375
Step 16: 6375 + 425 = 6800
Step 17: 6800 + 425 = 7225
Step 18: 7225 + 425 = 7650
Step 19: 7650 + 425 = 8075
Step 20: 8075 + 425 = 8500
Step 21: 8500 + 425 = 8925

So, 425*21 = 8925