Suppose you are studying economics. If you weren't studying economics, you would be studying literature, raising your grade in that class by a letter grade. If you weren't studying literature, you would be working, making $500. If you weren't working, you would be playing cards with friends. If you weren't playing cards with friends, you would be sleeping, which would improve your quiz score at your early-morning accounting class in the morning by 3 points. The opportunity cost of studying economics is