Let's roll up our sleeves and solve this. We have 721 and we're going to multiply it by 16, essentially adding 721 to itself 16 times.
Step 1: 0 + 721 = 721
Step 2: 721 + 721 = 1442
Step 3: 1442 + 721 = 2163
Step 4: 2163 + 721 = 2884
Step 5: 2884 + 721 = 3605
Step 6: 3605 + 721 = 4326
Step 7: 4326 + 721 = 5047
Step 8: 5047 + 721 = 5768
Step 9: 5768 + 721 = 6489
Step 10: 6489 + 721 = 7210
Step 11: 7210 + 721 = 7931
Step 12: 7931 + 721 = 8652
Step 13: 8652 + 721 = 9373
Step 14: 9373 + 721 = 10094
Step 15: 10094 + 721 = 10815
Step 16: 10815 + 721 = 11536

So, 721*16 = 11536