Alright, let's solve this math problem step by step. First, we have the number 273. Next, we see the multiplication sign, which means we need to multiply something. And what are we multiplying it by? We multiply it by 21. So, we're going to take the number 273 and add it to itself 21 times.
Step 1: 0 + 273 = 273
Step 2: 273 + 273 = 546
Step 3: 546 + 273 = 819
Step 4: 819 + 273 = 1092
Step 5: 1092 + 273 = 1365
Step 6: 1365 + 273 = 1638
Step 7: 1638 + 273 = 1911
Step 8: 1911 + 273 = 2184
Step 9: 2184 + 273 = 2457
Step 10: 2457 + 273 = 2730
Step 11: 2730 + 273 = 3003
Step 12: 3003 + 273 = 3276
Step 13: 3276 + 273 = 3549
Step 14: 3549 + 273 = 3822
Step 15: 3822 + 273 = 4095
Step 16: 4095 + 273 = 4368
Step 17: 4368 + 273 = 4641
Step 18: 4641 + 273 = 4914
Step 19: 4914 + 273 = 5187
Step 20: 5187 + 273 = 5460
Step 21: 5460 + 273 = 5733

So, 273*21 = 5733