Let's get this math done. We have 720 and we're going to multiply it by 80. This is the same as taking 720 and adding it to itself 80 times.
Step 1: 0 + 720 = 720
Step 2: 720 + 720 = 1440
Step 3: 1440 + 720 = 2160
Step 4: 2160 + 720 = 2880
Step 5: 2880 + 720 = 3600
Step 6: 3600 + 720 = 4320
Step 7: 4320 + 720 = 5040
Step 8: 5040 + 720 = 5760
Step 9: 5760 + 720 = 6480
Step 10: 6480 + 720 = 7200
Step 11: 7200 + 720 = 7920
Step 12: 7920 + 720 = 8640
Step 13: 8640 + 720 = 9360
Step 14: 9360 + 720 = 10080
Step 15: 10080 + 720 = 10800
Step 16: 10800 + 720 = 11520
Step 17: 11520 + 720 = 12240
Step 18: 12240 + 720 = 12960
Step 19: 12960 + 720 = 13680
Step 20: 13680 + 720 = 14400
Step 21: 14400 + 720 = 15120
Step 22: 15120 + 720 = 15840
Step 23: 15840 + 720 = 16560
Step 24: 16560 + 720 = 17280
Step 25: 17280 + 720 = 18000
Step 26: 18000 + 720 = 18720
Step 27: 18720 + 720 = 19440
Step 28: 19440 + 720 = 20160
Step 29: 20160 + 720 = 20880
Step 30: 20880 + 720 = 21600
Step 31: 21600 + 720 = 22320
Step 32: 22320 + 720 = 23040
Step 33: 23040 + 720 = 23760
Step 34: 23760 + 720 = 24480
Step 35: 24480 + 720 = 25200
Step 36: 25200 + 720 = 25920
Step 37: 25920 + 720 = 26640
Step 38: 26640 + 720 = 27360
Step 39: 27360 + 720 = 28080
Step 40: 28080 + 720 = 28800
Step 41: 28800 + 720 = 29520
Step 42: 29520 + 720 = 30240
Step 43: 30240 + 720 = 30960
Step 44: 30960 + 720 = 31680
Step 45: 31680 + 720 = 32400
Step 46: 32400 + 720 = 33120
Step 47: 33120 + 720 = 33840
Step 48: 33840 + 720 = 34560
Step 49: 34560 + 720 = 35280
Step 50: 35280 + 720 = 36000
Step 51: 36000 + 720 = 36720
Step 52: 36720 + 720 = 37440
Step 53: 37440 + 720 = 38160
Step 54: 38160 + 720 = 38880
Step 55: 38880 + 720 = 39600
Step 56: 39600 + 720 = 40320
Step 57: 40320 + 720 = 41040
Step 58: 41040 + 720 = 41760
Step 59: 41760 + 720 = 42480
Step 60: 42480 + 720 = 43200
Step 61: 43200 + 720 = 43920
Step 62: 43920 + 720 = 44640
Step 63: 44640 + 720 = 45360
Step 64: 45360 + 720 = 46080
Step 65: 46080 + 720 = 46800
Step 66: 46800 + 720 = 47520
Step 67: 47520 + 720 = 48240
Step 68: 48240 + 720 = 48960
Step 69: 48960 + 720 = 49680
Step 70: 49680 + 720 = 50400
Step 71: 50400 + 720 = 51120
Step 72: 51120 + 720 = 51840
Step 73: 51840 + 720 = 52560
Step 74: 52560 + 720 = 53280
Step 75: 53280 + 720 = 54000
Step 76: 54000 + 720 = 54720
Step 77: 54720 + 720 = 55440
Step 78: 55440 + 720 = 56160
Step 79: 56160 + 720 = 56880
Step 80: 56880 + 720 = 57600

So, 720*80 = 57600