Let's roll up our sleeves and solve this. We have 426 and we're going to multiply it by 20, essentially adding 426 to itself 20 times.
Step 1: 0 + 426 = 426
Step 2: 426 + 426 = 852
Step 3: 852 + 426 = 1278
Step 4: 1278 + 426 = 1704
Step 5: 1704 + 426 = 2130
Step 6: 2130 + 426 = 2556
Step 7: 2556 + 426 = 2982
Step 8: 2982 + 426 = 3408
Step 9: 3408 + 426 = 3834
Step 10: 3834 + 426 = 4260
Step 11: 4260 + 426 = 4686
Step 12: 4686 + 426 = 5112
Step 13: 5112 + 426 = 5538
Step 14: 5538 + 426 = 5964
Step 15: 5964 + 426 = 6390
Step 16: 6390 + 426 = 6816
Step 17: 6816 + 426 = 7242
Step 18: 7242 + 426 = 7668
Step 19: 7668 + 426 = 8094
Step 20: 8094 + 426 = 8520

So, 426*20 = 8520