COMMUTING TIMES Bill commutes to work in the business district of Boston. He takes the train 3/5 of the time and drives 2/5 of the time (when he visits clients). If he takes the train, then he gets home by 6:30 p.m. 85% of the time; if he drives, then he gets home by 6:30 p.m. 60% of the time. If Bill gets home by 6:30 p.m., what is the probability that he drove to work?