OK, let's crack this. We're given 850 and our task is to multiply it by 50. Essentially, we'll be adding 850 to itself 50 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

So, 850*50 = 42500