Sure thing! We've got 421 and we're gonna multiply it by 9. That's the same as adding 421 to itself 9 times.
Step 1: 0 + 421 = 421
Step 2: 421 + 421 = 842
Step 3: 842 + 421 = 1263
Step 4: 1263 + 421 = 1684
Step 5: 1684 + 421 = 2105
Step 6: 2105 + 421 = 2526
Step 7: 2526 + 421 = 2947
Step 8: 2947 + 421 = 3368
Step 9: 3368 + 421 = 3789

So, 421*9 = 3789