A plane traveled 972 miles to Berlin and back. The trip there was with the wind. It took 9 hours. The trip back was into the wind. The trip back took 18 hours. Find the speed of the plane in still air and the speed of the wind

With the wind, the plane's speed was (972 mi) / (9 h) = 108 mi/h.

Against the wind, the plane's speed was (972 mi) / (18 h) = 54 mi/h.

The speed of the plane in still air is the average of these speeds, 81 mi/h.

The speed of the wind is half the difference of the trip speeds, 27 mi/h.