A truck driver regularly drives round trips from A to B and then back to A. Each time he drives from A to B, he drives at a fixed speed that (in miles per hour) is uniformly distributed between 40 and 60; each time he drives from B to A, he drives at a fixed speed that is equally likely to be either 40 or 60.

(a) In the long run, what proportion of his driving time is spent going to B?

(b) In the long run, for what proportion of his driving time is he driving at a speed of 40 miles per hour?