Sure thing! We've got 213 and we're gonna multiply it by 21. That's the same as adding 213 to itself 21 times.
Step 1: 0 + 213 = 213
Step 2: 213 + 213 = 426
Step 3: 426 + 213 = 639
Step 4: 639 + 213 = 852
Step 5: 852 + 213 = 1065
Step 6: 1065 + 213 = 1278
Step 7: 1278 + 213 = 1491
Step 8: 1491 + 213 = 1704
Step 9: 1704 + 213 = 1917
Step 10: 1917 + 213 = 2130
Step 11: 2130 + 213 = 2343
Step 12: 2343 + 213 = 2556
Step 13: 2556 + 213 = 2769
Step 14: 2769 + 213 = 2982
Step 15: 2982 + 213 = 3195
Step 16: 3195 + 213 = 3408
Step 17: 3408 + 213 = 3621
Step 18: 3621 + 213 = 3834
Step 19: 3834 + 213 = 4047
Step 20: 4047 + 213 = 4260
Step 21: 4260 + 213 = 4473

So, 213*21 = 4473