An 80-kg crate is raised 2 m from the ground by a man who uses a rope and a system of pulleys. He exerts a force of 220 N on the rope and pulls a total of 8 m of rope through the pulleys while lifting the crate, which is at rest afterward. 

(a) How much work does the man do?

(b) What is the change in the potential energy of the crate? 

(c) If the answers to these questions are different, explain why.