physics help ?

Question

A student ( m=85 kg) runs up the stairs (h= 2.8 m) in 1.42 seconds.

a) Calculate the Energy change of the student.

b) Calculate the efficiency of the student if it took 9339 J of chemical potential energy for the student to run up the stairs 

c) Calculate the output power of the student in horsepower ( 1 h.p=746 W) 

Answer 1

work = mgh = 85•9.8•2.8 J

efficiency in perceht = 100(85•9.8•2.8/9339) =____%

power = work/time = 85•9.8•2.8/1.42 = ___ watts

or 85•9.8•2.8/1.42 watts x 1 HP/746 w = ___ HP