Alright, let's solve this math problem step by step. First, we have the number 321. Next, we see the multiplication sign, which means we need to multiply something. And what are we multiplying it by? We multiply it by 90. So, we're going to take the number 321 and add it to itself 90 times.
Step 1: 0 + 321 = 321
Step 2: 321 + 321 = 642
Step 3: 642 + 321 = 963
Step 4: 963 + 321 = 1284
Step 5: 1284 + 321 = 1605
Step 6: 1605 + 321 = 1926
Step 7: 1926 + 321 = 2247
Step 8: 2247 + 321 = 2568
Step 9: 2568 + 321 = 2889
Step 10: 2889 + 321 = 3210
Step 11: 3210 + 321 = 3531
Step 12: 3531 + 321 = 3852
Step 13: 3852 + 321 = 4173
Step 14: 4173 + 321 = 4494
Step 15: 4494 + 321 = 4815
Step 16: 4815 + 321 = 5136
Step 17: 5136 + 321 = 5457
Step 18: 5457 + 321 = 5778
Step 19: 5778 + 321 = 6099
Step 20: 6099 + 321 = 6420
Step 21: 6420 + 321 = 6741
Step 22: 6741 + 321 = 7062
Step 23: 7062 + 321 = 7383
Step 24: 7383 + 321 = 7704
Step 25: 7704 + 321 = 8025
Step 26: 8025 + 321 = 8346
Step 27: 8346 + 321 = 8667
Step 28: 8667 + 321 = 8988
Step 29: 8988 + 321 = 9309
Step 30: 9309 + 321 = 9630
Step 31: 9630 + 321 = 9951
Step 32: 9951 + 321 = 10272
Step 33: 10272 + 321 = 10593
Step 34: 10593 + 321 = 10914
Step 35: 10914 + 321 = 11235
Step 36: 11235 + 321 = 11556
Step 37: 11556 + 321 = 11877
Step 38: 11877 + 321 = 12198
Step 39: 12198 + 321 = 12519
Step 40: 12519 + 321 = 12840
Step 41: 12840 + 321 = 13161
Step 42: 13161 + 321 = 13482
Step 43: 13482 + 321 = 13803
Step 44: 13803 + 321 = 14124
Step 45: 14124 + 321 = 14445
Step 46: 14445 + 321 = 14766
Step 47: 14766 + 321 = 15087
Step 48: 15087 + 321 = 15408
Step 49: 15408 + 321 = 15729
Step 50: 15729 + 321 = 16050
Step 51: 16050 + 321 = 16371
Step 52: 16371 + 321 = 16692
Step 53: 16692 + 321 = 17013
Step 54: 17013 + 321 = 17334
Step 55: 17334 + 321 = 17655
Step 56: 17655 + 321 = 17976
Step 57: 17976 + 321 = 18297
Step 58: 18297 + 321 = 18618
Step 59: 18618 + 321 = 18939
Step 60: 18939 + 321 = 19260
Step 61: 19260 + 321 = 19581
Step 62: 19581 + 321 = 19902
Step 63: 19902 + 321 = 20223
Step 64: 20223 + 321 = 20544
Step 65: 20544 + 321 = 20865
Step 66: 20865 + 321 = 21186
Step 67: 21186 + 321 = 21507
Step 68: 21507 + 321 = 21828
Step 69: 21828 + 321 = 22149
Step 70: 22149 + 321 = 22470
Step 71: 22470 + 321 = 22791
Step 72: 22791 + 321 = 23112
Step 73: 23112 + 321 = 23433
Step 74: 23433 + 321 = 23754
Step 75: 23754 + 321 = 24075
Step 76: 24075 + 321 = 24396
Step 77: 24396 + 321 = 24717
Step 78: 24717 + 321 = 25038
Step 79: 25038 + 321 = 25359
Step 80: 25359 + 321 = 25680
Step 81: 25680 + 321 = 26001
Step 82: 26001 + 321 = 26322
Step 83: 26322 + 321 = 26643
Step 84: 26643 + 321 = 26964
Step 85: 26964 + 321 = 27285
Step 86: 27285 + 321 = 27606
Step 87: 27606 + 321 = 27927
Step 88: 27927 + 321 = 28248
Step 89: 28248 + 321 = 28569
Step 90: 28569 + 321 = 28890

So, 321*90 = 28890