Without delay, let's solve this. We've got 739 and we will be multiplying it by 21, that is, adding 739 to itself 21 times.
Step 1: 0 + 739 = 739
Step 2: 739 + 739 = 1478
Step 3: 1478 + 739 = 2217
Step 4: 2217 + 739 = 2956
Step 5: 2956 + 739 = 3695
Step 6: 3695 + 739 = 4434
Step 7: 4434 + 739 = 5173
Step 8: 5173 + 739 = 5912
Step 9: 5912 + 739 = 6651
Step 10: 6651 + 739 = 7390
Step 11: 7390 + 739 = 8129
Step 12: 8129 + 739 = 8868
Step 13: 8868 + 739 = 9607
Step 14: 9607 + 739 = 10346
Step 15: 10346 + 739 = 11085
Step 16: 11085 + 739 = 11824
Step 17: 11824 + 739 = 12563
Step 18: 12563 + 739 = 13302
Step 19: 13302 + 739 = 14041
Step 20: 14041 + 739 = 14780
Step 21: 14780 + 739 = 15519

So, 739*21 = 15519