A swimmer wants to cross a river, from point A to point B, as shown in the figure. The distance d1 (from A to C) is 200 m, the distance d2 (from C to B) is 150 m, and the speed vr of the current in the river is 5 km/hour. Suppose that the swimmer's velocity relative to the water makes an angle of 45 degrees with the line from A to C, as indicated in the figure. To swim directly from A to B, what speed relative to the water, should the swimmer have?
