A weightlifter works out at the gym each day. Part of her routine is to lie on her back and lift a 40 kg barbell straight up from chest height to full arm extension, a distance of 0.50 m. 

a. How much work does the weightlifter do to lift the barbell one time? 

b. If the weightlifter does 20 repetitions a day, what total energy does she expend on lifting, assuming a typical efficiency for energy use by the body. 

c. How many 400 Calorie donuts can she eat a day to supply that energy?