Let's roll up our sleeves and solve this. We have 457 and we're going to multiply it by 20, essentially adding 457 to itself 20 times.
Step 1: 0 + 457 = 457
Step 2: 457 + 457 = 914
Step 3: 914 + 457 = 1371
Step 4: 1371 + 457 = 1828
Step 5: 1828 + 457 = 2285
Step 6: 2285 + 457 = 2742
Step 7: 2742 + 457 = 3199
Step 8: 3199 + 457 = 3656
Step 9: 3656 + 457 = 4113
Step 10: 4113 + 457 = 4570
Step 11: 4570 + 457 = 5027
Step 12: 5027 + 457 = 5484
Step 13: 5484 + 457 = 5941
Step 14: 5941 + 457 = 6398
Step 15: 6398 + 457 = 6855
Step 16: 6855 + 457 = 7312
Step 17: 7312 + 457 = 7769
Step 18: 7769 + 457 = 8226
Step 19: 8226 + 457 = 8683
Step 20: 8683 + 457 = 9140

So, 457*20 = 9140