You're the monopoly owner of a movie theater with two customers, Thelma and Louise. Thelma doesn't care

Question:

You're the monopoly owner of a movie theater with two customers, Thelma and Louise. Thelma doesn't care at all about the movie; she just comes to buy popcorn. Louise doesn't like popcorn; she just comes to watch the movie.
Thelma's demand curve for popcorn is as shown in the graph below. Louise is willing to pay up to A + B + C to see the movie. It costs you 50¢ a bag to provide the popcorn. You're deciding whether to sell it for 50¢ a bag or for 40¢ a bag. Which of the illustrated areas in the graph would you want to measure to help you make your decision, and exactly how would you use thatinformation?