(a) What is the efficiency of an out-of-condition professor who does 2.10 x 103 J of useful work while metabolizing 500 kcal of food energy? (Enter your answer as a percentage. Enter a number.) % (b) How many food calories (in kcal) would a well-conditioned athlete metabolize in doing the same work with an efficiency of 20%? (Enter a number.) kcal