An 80-kg physics student climbs a 120-m hill.

(a) What is the increase in the gravitational potential energy of the student?

(b) Where does this energy come from?

(c) The student's body is 20% efficient; that is, for every 20 J that are converted to mechanical energy, 100 J of internal energy are expended, with 80 J going into thermal energy. How much chemical energy is expended by the student during the climb?