Alright, let's solve this math problem step by step. First, we have the number 239. 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 239 and add it to itself 21 times.
Step 1: 0 + 239 = 239
Step 2: 239 + 239 = 478
Step 3: 478 + 239 = 717
Step 4: 717 + 239 = 956
Step 5: 956 + 239 = 1195
Step 6: 1195 + 239 = 1434
Step 7: 1434 + 239 = 1673
Step 8: 1673 + 239 = 1912
Step 9: 1912 + 239 = 2151
Step 10: 2151 + 239 = 2390
Step 11: 2390 + 239 = 2629
Step 12: 2629 + 239 = 2868
Step 13: 2868 + 239 = 3107
Step 14: 3107 + 239 = 3346
Step 15: 3346 + 239 = 3585
Step 16: 3585 + 239 = 3824
Step 17: 3824 + 239 = 4063
Step 18: 4063 + 239 = 4302
Step 19: 4302 + 239 = 4541
Step 20: 4541 + 239 = 4780
Step 21: 4780 + 239 = 5019

So, 239*21 = 5019