The label on a candy bar says 470 Calories.Assuming a typical efficiency for energy use by the body, if a 74 kg person were to use the energy in this candy bar to climb stairs, how high could she go?

Answer 1

Exactly what is a "typical efficiency"? Is that a physics term? (Answer:NO)

Labels on candy bars are in food Calories, which is not your obselete physics term "calories". Look up the difference.

Now to answer your question (sort of). Disect it to understand. It assumes 100 percent efficiency

mgh=1000*470* 4.18 check the units.

h= 1000*470*4.18/((74*9.8)) which is plenty high. Now you are at your "typical efficiency" term.
One can "burn" off 470 Calories by about one hour on a stationary bike with moderate effort.
http://www.nutristrategy.com/activitylist.htm

Most of the energy consumed by the body goes to keeping the heart running, and the body warm.

Answer 2

typical efficiency = .25= 25%