Sure thing, let's get straight to it. We start with 681 and we're going to multiply it by 21, which means adding 681 to itself 21 times.
Step 1: 0 + 681 = 681
Step 2: 681 + 681 = 1362
Step 3: 1362 + 681 = 2043
Step 4: 2043 + 681 = 2724
Step 5: 2724 + 681 = 3405
Step 6: 3405 + 681 = 4086
Step 7: 4086 + 681 = 4767
Step 8: 4767 + 681 = 5448
Step 9: 5448 + 681 = 6129
Step 10: 6129 + 681 = 6810
Step 11: 6810 + 681 = 7491
Step 12: 7491 + 681 = 8172
Step 13: 8172 + 681 = 8853
Step 14: 8853 + 681 = 9534
Step 15: 9534 + 681 = 10215
Step 16: 10215 + 681 = 10896
Step 17: 10896 + 681 = 11577
Step 18: 11577 + 681 = 12258
Step 19: 12258 + 681 = 12939
Step 20: 12939 + 681 = 13620
Step 21: 13620 + 681 = 14301

So, 681*21 = 14301