A boy is attempting to swim directly across a river; he is able to swim at a

Question:

A boy is attempting to swim directly across a river; he is able to swim at a speed of 0.500 m/s relative to the water. The river is 25.0 m wide and the boy ends up at 50.0 m downstream from his starting point.
(a) How fast is the current flowing in the river?
(b) What is the speed of the boy relative to a friend standing on the riverbank?