The same young man (with a mass of 68 kg) decides to work off the excess calories by carrying 5-gallon buckets of water (assume each bucket is 16 kg) from his retention pond up. If he lifts each bucket to a height of 2 meters and he has to carry 10 buckets up every hour, what is the minimum power he needs to exert?
a) 320 W
b) 480 W
c) 640 W
d) 800 W