A jet skier wants to travel 5km (w20s) to an island in a river, the river is flowing 6 km/hr east. If his SPEED is 40 km/hr relative to the water:

A)what direction must he head his jet ski to get to his location

B)how long will it take?

The book answers are (w17s) and 8.7 min

I have no idea how to ge to this answer , any help?