Alright, let's solve this math problem step by step. First, we have the number 28. Next, we see the multiplication sign, which means we need to multiply something. And what are we multiplying it by? We multiply it by 23. So, we're going to take the number 28 and add it to itself 23 times.
Step 1: 0 + 28 = 28
Step 2: 28 + 28 = 56
Step 3: 56 + 28 = 84
Step 4: 84 + 28 = 112
Step 5: 112 + 28 = 140
Step 6: 140 + 28 = 168
Step 7: 168 + 28 = 196
Step 8: 196 + 28 = 224
Step 9: 224 + 28 = 252
Step 10: 252 + 28 = 280
Step 11: 280 + 28 = 308
Step 12: 308 + 28 = 336
Step 13: 336 + 28 = 364
Step 14: 364 + 28 = 392
Step 15: 392 + 28 = 420
Step 16: 420 + 28 = 448
Step 17: 448 + 28 = 476
Step 18: 476 + 28 = 504
Step 19: 504 + 28 = 532
Step 20: 532 + 28 = 560
Step 21: 560 + 28 = 588
Step 22: 588 + 28 = 616
Step 23: 616 + 28 = 644

So, 28*23 = 644