Outboard Speed Boats An Outboard Motor Boat Can Pull A Water Skier At A Cruising Speed Of 28mi/h In Still Water?

An outboard motor boat can pull a water skier at a cruising speed of 28mi/h in still water? - outboard speed boats

A boat with an outboard motor is a water-skier at a cruising speed of 28mi / h drag in calm water. The boat has a ski pass for a ride on a river that by 6Mi / h. The boat has a water-skier and then goes home. The trip takes an hour. How to travel further upstream?