A Kolasaraptor is standing at the edge of a slow-moving, 30 mile wide river. He wants to return to his lair in the opposite side of the river and 100 miles downstream from the point directly across from the river from his starting point. Assume that the Kolasaraptor can run 6 miles per hour and swim 4 miles per hour. How far should he run to minimize his total travel time (assume the speed of the river is negligible)?

Question

A Kolasaraptor is standing at the edge of a slow-moving, 30 mile wide river.  He wants to return to his lair in the opposite side of the river and 100 miles downstream from the point directly across from the river from his starting point.  Assume that the Kolasaraptor can run 6 miles per hour and swim 4 miles per hour.  How far should he run to minimize his total travel time (assume the speed of the river is negligible)?