Sure thing! We've got 396 and we're gonna multiply it by 21. That's the same as adding 396 to itself 21 times.
Step 1: 0 + 396 = 396
Step 2: 396 + 396 = 792
Step 3: 792 + 396 = 1188
Step 4: 1188 + 396 = 1584
Step 5: 1584 + 396 = 1980
Step 6: 1980 + 396 = 2376
Step 7: 2376 + 396 = 2772
Step 8: 2772 + 396 = 3168
Step 9: 3168 + 396 = 3564
Step 10: 3564 + 396 = 3960
Step 11: 3960 + 396 = 4356
Step 12: 4356 + 396 = 4752
Step 13: 4752 + 396 = 5148
Step 14: 5148 + 396 = 5544
Step 15: 5544 + 396 = 5940
Step 16: 5940 + 396 = 6336
Step 17: 6336 + 396 = 6732
Step 18: 6732 + 396 = 7128
Step 19: 7128 + 396 = 7524
Step 20: 7524 + 396 = 7920
Step 21: 7920 + 396 = 8316

So, 396*21 = 8316