9 Betty and Anna work at the same office in Brussels. They both must attend a meeting in Paris, so they decide to drive to the meeting together. Betty is a cigarette smoker, and her marginal benefit from smoking a packet of cigarettes a day is €40. Cigarettes are €6 a packet. Anna dislikes cigarette smoke, and her marginal benefit from a smoke-free environment is €50 a day. What is the outcome if:

a Betty drives her car with Anna as a passenger?

b Anna drives her car with Betty as a passenger?