OK, let's work through this together. We're starting with 279 and we're going to multiply it by 21, which means we add 279 to itself 21 times.
Step 1: 0 + 279 = 279
Step 2: 279 + 279 = 558
Step 3: 558 + 279 = 837
Step 4: 837 + 279 = 1116
Step 5: 1116 + 279 = 1395
Step 6: 1395 + 279 = 1674
Step 7: 1674 + 279 = 1953
Step 8: 1953 + 279 = 2232
Step 9: 2232 + 279 = 2511
Step 10: 2511 + 279 = 2790
Step 11: 2790 + 279 = 3069
Step 12: 3069 + 279 = 3348
Step 13: 3348 + 279 = 3627
Step 14: 3627 + 279 = 3906
Step 15: 3906 + 279 = 4185
Step 16: 4185 + 279 = 4464
Step 17: 4464 + 279 = 4743
Step 18: 4743 + 279 = 5022
Step 19: 5022 + 279 = 5301
Step 20: 5301 + 279 = 5580
Step 21: 5580 + 279 = 5859

So, 279*21 = 5859