An athlete crosses a 21 m wide river by swimming perpendicular to the water current at a speed of 0.45 m/s relative to the water. He reaches the opposite side at a distance 44 m downstream from his starting point. a) How fast is the water in the river flowing with respect to the ground in m/s?

b) What is the speed of the swimmer with respect to a friend at rest on the ground in m/s?