Betty and Anna work at the same office in Philadelphia and they have to attend a meeting in Pittsburgh. They decide to drive to the out-oftown meeting together. Betty is a cigarette smoker and when she smokes a pack of cigarettes a day her marginal benefit is $40. Cigarettes are $6 a pack. Anna dislikes cigarette smoke, and her marginal benefit of 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?