Without delay, let's solve this. We've got 794 and we will be multiplying it by 21, that is, adding 794 to itself 21 times.
Step 1: 0 + 794 = 794
Step 2: 794 + 794 = 1588
Step 3: 1588 + 794 = 2382
Step 4: 2382 + 794 = 3176
Step 5: 3176 + 794 = 3970
Step 6: 3970 + 794 = 4764
Step 7: 4764 + 794 = 5558
Step 8: 5558 + 794 = 6352
Step 9: 6352 + 794 = 7146
Step 10: 7146 + 794 = 7940
Step 11: 7940 + 794 = 8734
Step 12: 8734 + 794 = 9528
Step 13: 9528 + 794 = 10322
Step 14: 10322 + 794 = 11116
Step 15: 11116 + 794 = 11910
Step 16: 11910 + 794 = 12704
Step 17: 12704 + 794 = 13498
Step 18: 13498 + 794 = 14292
Step 19: 14292 + 794 = 15086
Step 20: 15086 + 794 = 15880
Step 21: 15880 + 794 = 16674

So, 794*21 = 16674