A river has a constant current of 3 km/hr. At what angle to a boat dock should

Question:

A river has a constant current of 3 km/hr. At what angle to a boat dock should a motorboat capable of maintaining a constant speed of 20 km/hr be headed in order to reach a point directly opposite the dock? If the river is 1/2kilometer wide, how long will it take to cross? Current - Boat Direction of boat due to current