Sure thing! We've got 971 and we're gonna multiply it by 21. That's the same as adding 971 to itself 21 times.
Step 1: 0 + 971 = 971
Step 2: 971 + 971 = 1942
Step 3: 1942 + 971 = 2913
Step 4: 2913 + 971 = 3884
Step 5: 3884 + 971 = 4855
Step 6: 4855 + 971 = 5826
Step 7: 5826 + 971 = 6797
Step 8: 6797 + 971 = 7768
Step 9: 7768 + 971 = 8739
Step 10: 8739 + 971 = 9710
Step 11: 9710 + 971 = 10681
Step 12: 10681 + 971 = 11652
Step 13: 11652 + 971 = 12623
Step 14: 12623 + 971 = 13594
Step 15: 13594 + 971 = 14565
Step 16: 14565 + 971 = 15536
Step 17: 15536 + 971 = 16507
Step 18: 16507 + 971 = 17478
Step 19: 17478 + 971 = 18449
Step 20: 18449 + 971 = 19420
Step 21: 19420 + 971 = 20391

So, 971*21 = 20391