OK, let's work through this together. We're starting with 99 and we're going to multiply it by 45, which means we add 99 to itself 45 times.
Step 1: 0 + 99 = 99
Step 2: 99 + 99 = 198
Step 3: 198 + 99 = 297
Step 4: 297 + 99 = 396
Step 5: 396 + 99 = 495
Step 6: 495 + 99 = 594
Step 7: 594 + 99 = 693
Step 8: 693 + 99 = 792
Step 9: 792 + 99 = 891
Step 10: 891 + 99 = 990
Step 11: 990 + 99 = 1089
Step 12: 1089 + 99 = 1188
Step 13: 1188 + 99 = 1287
Step 14: 1287 + 99 = 1386
Step 15: 1386 + 99 = 1485
Step 16: 1485 + 99 = 1584
Step 17: 1584 + 99 = 1683
Step 18: 1683 + 99 = 1782
Step 19: 1782 + 99 = 1881
Step 20: 1881 + 99 = 1980
Step 21: 1980 + 99 = 2079
Step 22: 2079 + 99 = 2178
Step 23: 2178 + 99 = 2277
Step 24: 2277 + 99 = 2376
Step 25: 2376 + 99 = 2475
Step 26: 2475 + 99 = 2574
Step 27: 2574 + 99 = 2673
Step 28: 2673 + 99 = 2772
Step 29: 2772 + 99 = 2871
Step 30: 2871 + 99 = 2970
Step 31: 2970 + 99 = 3069
Step 32: 3069 + 99 = 3168
Step 33: 3168 + 99 = 3267
Step 34: 3267 + 99 = 3366
Step 35: 3366 + 99 = 3465
Step 36: 3465 + 99 = 3564
Step 37: 3564 + 99 = 3663
Step 38: 3663 + 99 = 3762
Step 39: 3762 + 99 = 3861
Step 40: 3861 + 99 = 3960
Step 41: 3960 + 99 = 4059
Step 42: 4059 + 99 = 4158
Step 43: 4158 + 99 = 4257
Step 44: 4257 + 99 = 4356
Step 45: 4356 + 99 = 4455

So, 99*45 = 4455