【单选题】Joe likes to sleep late in the mornings and play tennis in the afternoons. The opportunity cost of Joe attending his morning class for one hour is
【单选题】Joe's budget constraint equals 500 = 2F + 100S, where $500 is Joe's income, $2 is the price of food (F) and $100 is the price of shelter (S). How much food can Joe buy if he buys one unit of shelter?