Anna has four choices. In 2 hours of her time, she can study, go to the movies, tutor someone or work at the bakery. If she studies, her marginal benefit would be $90 and her explicit marginal cost would be $30. If she goes to the movies, her marginal benefit would be $50 and her explicit marginal cost would be $10. If she tutors someone, her marginal benefit would be $100 and her explicit marginal cost would be $50. If she works at the bakery, her marginal benefit would be $70 and her explicit marginal cost would be $40.

a. Assuming that Anna is rational, what should she do?