Let's roll up our sleeves and solve this. We have 850 and we're going to multiply it by 100, essentially adding 850 to itself 100 times.
Step 1: 0 + 850 = 850
Step 2: 850 + 850 = 1700
Step 3: 1700 + 850 = 2550
Step 4: 2550 + 850 = 3400
Step 5: 3400 + 850 = 4250
Step 6: 4250 + 850 = 5100
Step 7: 5100 + 850 = 5950
Step 8: 5950 + 850 = 6800
Step 9: 6800 + 850 = 7650
Step 10: 7650 + 850 = 8500
Step 11: 8500 + 850 = 9350
Step 12: 9350 + 850 = 10200
Step 13: 10200 + 850 = 11050
Step 14: 11050 + 850 = 11900
Step 15: 11900 + 850 = 12750
Step 16: 12750 + 850 = 13600
Step 17: 13600 + 850 = 14450
Step 18: 14450 + 850 = 15300
Step 19: 15300 + 850 = 16150
Step 20: 16150 + 850 = 17000
Step 21: 17000 + 850 = 17850
Step 22: 17850 + 850 = 18700
Step 23: 18700 + 850 = 19550
Step 24: 19550 + 850 = 20400
Step 25: 20400 + 850 = 21250
Step 26: 21250 + 850 = 22100
Step 27: 22100 + 850 = 22950
Step 28: 22950 + 850 = 23800
Step 29: 23800 + 850 = 24650
Step 30: 24650 + 850 = 25500
Step 31: 25500 + 850 = 26350
Step 32: 26350 + 850 = 27200
Step 33: 27200 + 850 = 28050
Step 34: 28050 + 850 = 28900
Step 35: 28900 + 850 = 29750
Step 36: 29750 + 850 = 30600
Step 37: 30600 + 850 = 31450
Step 38: 31450 + 850 = 32300
Step 39: 32300 + 850 = 33150
Step 40: 33150 + 850 = 34000
Step 41: 34000 + 850 = 34850
Step 42: 34850 + 850 = 35700
Step 43: 35700 + 850 = 36550
Step 44: 36550 + 850 = 37400
Step 45: 37400 + 850 = 38250
Step 46: 38250 + 850 = 39100
Step 47: 39100 + 850 = 39950
Step 48: 39950 + 850 = 40800
Step 49: 40800 + 850 = 41650
Step 50: 41650 + 850 = 42500
Step 51: 42500 + 850 = 43350
Step 52: 43350 + 850 = 44200
Step 53: 44200 + 850 = 45050
Step 54: 45050 + 850 = 45900
Step 55: 45900 + 850 = 46750
Step 56: 46750 + 850 = 47600
Step 57: 47600 + 850 = 48450
Step 58: 48450 + 850 = 49300
Step 59: 49300 + 850 = 50150
Step 60: 50150 + 850 = 51000
Step 61: 51000 + 850 = 51850
Step 62: 51850 + 850 = 52700
Step 63: 52700 + 850 = 53550
Step 64: 53550 + 850 = 54400
Step 65: 54400 + 850 = 55250
Step 66: 55250 + 850 = 56100
Step 67: 56100 + 850 = 56950
Step 68: 56950 + 850 = 57800
Step 69: 57800 + 850 = 58650
Step 70: 58650 + 850 = 59500
Step 71: 59500 + 850 = 60350
Step 72: 60350 + 850 = 61200
Step 73: 61200 + 850 = 62050
Step 74: 62050 + 850 = 62900
Step 75: 62900 + 850 = 63750
Step 76: 63750 + 850 = 64600
Step 77: 64600 + 850 = 65450
Step 78: 65450 + 850 = 66300
Step 79: 66300 + 850 = 67150
Step 80: 67150 + 850 = 68000
Step 81: 68000 + 850 = 68850
Step 82: 68850 + 850 = 69700
Step 83: 69700 + 850 = 70550
Step 84: 70550 + 850 = 71400
Step 85: 71400 + 850 = 72250
Step 86: 72250 + 850 = 73100
Step 87: 73100 + 850 = 73950
Step 88: 73950 + 850 = 74800
Step 89: 74800 + 850 = 75650
Step 90: 75650 + 850 = 76500
Step 91: 76500 + 850 = 77350
Step 92: 77350 + 850 = 78200
Step 93: 78200 + 850 = 79050
Step 94: 79050 + 850 = 79900
Step 95: 79900 + 850 = 80750
Step 96: 80750 + 850 = 81600
Step 97: 81600 + 850 = 82450
Step 98: 82450 + 850 = 83300
Step 99: 83300 + 850 = 84150
Step 100: 84150 + 850 = 85000

So, 850*100 = 85000