Let's get this math done. We have 825 and we're going to multiply it by 42. This is the same as taking 825 and adding it to itself 42 times.
Step 1: 0 + 825 = 825
Step 2: 825 + 825 = 1650
Step 3: 1650 + 825 = 2475
Step 4: 2475 + 825 = 3300
Step 5: 3300 + 825 = 4125
Step 6: 4125 + 825 = 4950
Step 7: 4950 + 825 = 5775
Step 8: 5775 + 825 = 6600
Step 9: 6600 + 825 = 7425
Step 10: 7425 + 825 = 8250
Step 11: 8250 + 825 = 9075
Step 12: 9075 + 825 = 9900
Step 13: 9900 + 825 = 10725
Step 14: 10725 + 825 = 11550
Step 15: 11550 + 825 = 12375
Step 16: 12375 + 825 = 13200
Step 17: 13200 + 825 = 14025
Step 18: 14025 + 825 = 14850
Step 19: 14850 + 825 = 15675
Step 20: 15675 + 825 = 16500
Step 21: 16500 + 825 = 17325
Step 22: 17325 + 825 = 18150
Step 23: 18150 + 825 = 18975
Step 24: 18975 + 825 = 19800
Step 25: 19800 + 825 = 20625
Step 26: 20625 + 825 = 21450
Step 27: 21450 + 825 = 22275
Step 28: 22275 + 825 = 23100
Step 29: 23100 + 825 = 23925
Step 30: 23925 + 825 = 24750
Step 31: 24750 + 825 = 25575
Step 32: 25575 + 825 = 26400
Step 33: 26400 + 825 = 27225
Step 34: 27225 + 825 = 28050
Step 35: 28050 + 825 = 28875
Step 36: 28875 + 825 = 29700
Step 37: 29700 + 825 = 30525
Step 38: 30525 + 825 = 31350
Step 39: 31350 + 825 = 32175
Step 40: 32175 + 825 = 33000
Step 41: 33000 + 825 = 33825
Step 42: 33825 + 825 = 34650

So, 825*42 = 34650