Let's roll up our sleeves and solve this. We have 160 and we're going to multiply it by 81, essentially adding 160 to itself 81 times.
Step 1: 0 + 160 = 160
Step 2: 160 + 160 = 320
Step 3: 320 + 160 = 480
Step 4: 480 + 160 = 640
Step 5: 640 + 160 = 800
Step 6: 800 + 160 = 960
Step 7: 960 + 160 = 1120
Step 8: 1120 + 160 = 1280
Step 9: 1280 + 160 = 1440
Step 10: 1440 + 160 = 1600
Step 11: 1600 + 160 = 1760
Step 12: 1760 + 160 = 1920
Step 13: 1920 + 160 = 2080
Step 14: 2080 + 160 = 2240
Step 15: 2240 + 160 = 2400
Step 16: 2400 + 160 = 2560
Step 17: 2560 + 160 = 2720
Step 18: 2720 + 160 = 2880
Step 19: 2880 + 160 = 3040
Step 20: 3040 + 160 = 3200
Step 21: 3200 + 160 = 3360
Step 22: 3360 + 160 = 3520
Step 23: 3520 + 160 = 3680
Step 24: 3680 + 160 = 3840
Step 25: 3840 + 160 = 4000
Step 26: 4000 + 160 = 4160
Step 27: 4160 + 160 = 4320
Step 28: 4320 + 160 = 4480
Step 29: 4480 + 160 = 4640
Step 30: 4640 + 160 = 4800
Step 31: 4800 + 160 = 4960
Step 32: 4960 + 160 = 5120
Step 33: 5120 + 160 = 5280
Step 34: 5280 + 160 = 5440
Step 35: 5440 + 160 = 5600
Step 36: 5600 + 160 = 5760
Step 37: 5760 + 160 = 5920
Step 38: 5920 + 160 = 6080
Step 39: 6080 + 160 = 6240
Step 40: 6240 + 160 = 6400
Step 41: 6400 + 160 = 6560
Step 42: 6560 + 160 = 6720
Step 43: 6720 + 160 = 6880
Step 44: 6880 + 160 = 7040
Step 45: 7040 + 160 = 7200
Step 46: 7200 + 160 = 7360
Step 47: 7360 + 160 = 7520
Step 48: 7520 + 160 = 7680
Step 49: 7680 + 160 = 7840
Step 50: 7840 + 160 = 8000
Step 51: 8000 + 160 = 8160
Step 52: 8160 + 160 = 8320
Step 53: 8320 + 160 = 8480
Step 54: 8480 + 160 = 8640
Step 55: 8640 + 160 = 8800
Step 56: 8800 + 160 = 8960
Step 57: 8960 + 160 = 9120
Step 58: 9120 + 160 = 9280
Step 59: 9280 + 160 = 9440
Step 60: 9440 + 160 = 9600
Step 61: 9600 + 160 = 9760
Step 62: 9760 + 160 = 9920
Step 63: 9920 + 160 = 10080
Step 64: 10080 + 160 = 10240
Step 65: 10240 + 160 = 10400
Step 66: 10400 + 160 = 10560
Step 67: 10560 + 160 = 10720
Step 68: 10720 + 160 = 10880
Step 69: 10880 + 160 = 11040
Step 70: 11040 + 160 = 11200
Step 71: 11200 + 160 = 11360
Step 72: 11360 + 160 = 11520
Step 73: 11520 + 160 = 11680
Step 74: 11680 + 160 = 11840
Step 75: 11840 + 160 = 12000
Step 76: 12000 + 160 = 12160
Step 77: 12160 + 160 = 12320
Step 78: 12320 + 160 = 12480
Step 79: 12480 + 160 = 12640
Step 80: 12640 + 160 = 12800
Step 81: 12800 + 160 = 12960

So, 160*81 = 12960