OK, let's crack this. We're given 800 and our task is to multiply it by 45. Essentially, we'll be adding 800 to itself 45 times.
Step 1: 0 + 800 = 800
Step 2: 800 + 800 = 1600
Step 3: 1600 + 800 = 2400
Step 4: 2400 + 800 = 3200
Step 5: 3200 + 800 = 4000
Step 6: 4000 + 800 = 4800
Step 7: 4800 + 800 = 5600
Step 8: 5600 + 800 = 6400
Step 9: 6400 + 800 = 7200
Step 10: 7200 + 800 = 8000
Step 11: 8000 + 800 = 8800
Step 12: 8800 + 800 = 9600
Step 13: 9600 + 800 = 10400
Step 14: 10400 + 800 = 11200
Step 15: 11200 + 800 = 12000
Step 16: 12000 + 800 = 12800
Step 17: 12800 + 800 = 13600
Step 18: 13600 + 800 = 14400
Step 19: 14400 + 800 = 15200
Step 20: 15200 + 800 = 16000
Step 21: 16000 + 800 = 16800
Step 22: 16800 + 800 = 17600
Step 23: 17600 + 800 = 18400
Step 24: 18400 + 800 = 19200
Step 25: 19200 + 800 = 20000
Step 26: 20000 + 800 = 20800
Step 27: 20800 + 800 = 21600
Step 28: 21600 + 800 = 22400
Step 29: 22400 + 800 = 23200
Step 30: 23200 + 800 = 24000
Step 31: 24000 + 800 = 24800
Step 32: 24800 + 800 = 25600
Step 33: 25600 + 800 = 26400
Step 34: 26400 + 800 = 27200
Step 35: 27200 + 800 = 28000
Step 36: 28000 + 800 = 28800
Step 37: 28800 + 800 = 29600
Step 38: 29600 + 800 = 30400
Step 39: 30400 + 800 = 31200
Step 40: 31200 + 800 = 32000
Step 41: 32000 + 800 = 32800
Step 42: 32800 + 800 = 33600
Step 43: 33600 + 800 = 34400
Step 44: 34400 + 800 = 35200
Step 45: 35200 + 800 = 36000

So, 800*45 = 36000