An athlete in a competition needs to get from point A to another point B directly across from a river. He can swim in stationary water at a speed of 2.0 mi/h, and he can run at a speed of 5.0 mi/h. If the river does not flow, then to get from A to B he would certainly choose to swim directly across. But the river flows at a speed of 1.5 mi/h downstream. Given that, what would his strategy be in order to minimize the total time it takes to move from A to B? i.e., at what angle upstream (measured from the line AB) should he be swimming?