A camera operator is filming a nature explorer in the Rocky Mountains. The explorer needs to swim across a river to his campsite. By watching debris flowing down the river, the operator estimates that the stream is flowing at 0.633 m/s0.633 m/s . In still water, the explorer can swim at 0.739 m/s0.739 m/s . At what angle, less than 90°, with respect to the shoreline should the operator advise him to swim so that he travels directly across the stream to his campfire?