The first trip had an average speed of (175 mi)/(7/6 h) = 150 mi/h
The second trip had an average speed of (175 mi)/(5/6 h) = 210 mi/h
The speed of the plane in still air is (150 +210)/2 = 180 mi/h. The speed of the wind is 180 -150 = 30 mi/h.
_____ The two trip speeds are the sum and difference of the speed of the plane and the speed of the wind. Let p and w represent the speeds of plane and wind, respectively. p -w = 150 mph p +w = 210 mph Adding these two equations gives 2p = (150 +210) mph p = (150 +210)/2 mph = 180 mph Then, from the first equation, p -150 mph = w (180 -150) mph = w = 30 mph