OK, let's crack this. We're given 511 and our task is to multiply it by 21. Essentially, we'll be adding 511 to itself 21 times.
Step 1: 0 + 511 = 511
Step 2: 511 + 511 = 1022
Step 3: 1022 + 511 = 1533
Step 4: 1533 + 511 = 2044
Step 5: 2044 + 511 = 2555
Step 6: 2555 + 511 = 3066
Step 7: 3066 + 511 = 3577
Step 8: 3577 + 511 = 4088
Step 9: 4088 + 511 = 4599
Step 10: 4599 + 511 = 5110
Step 11: 5110 + 511 = 5621
Step 12: 5621 + 511 = 6132
Step 13: 6132 + 511 = 6643
Step 14: 6643 + 511 = 7154
Step 15: 7154 + 511 = 7665
Step 16: 7665 + 511 = 8176
Step 17: 8176 + 511 = 8687
Step 18: 8687 + 511 = 9198
Step 19: 9198 + 511 = 9709
Step 20: 9709 + 511 = 10220
Step 21: 10220 + 511 = 10731

So, 511*21 = 10731