A plane flies 720 mi against a steady 30-mi/h headwind and then returns to the same point with the wind. If the entire trip takes 10 h, what is the plane’s speed in still air?

A plane flies 720 mi against a steady 30-mi/h headwindand then returns to the same point with the wind. If the entire trip takes 10 h, whatis the plane’s speed in still air?