Let p and w represent the speed of the plane and the speed of the wind, respectively. .. speed = distance/time .. p +w = 720/3 = 240 .. p -w = 720/4 = 180
Add the two equations to eliminate w. .. 2p = 420 .. p = 210 .. w = p -180 = 30
The speed of the wind is 30 mph. The speed of the plane in still air is 210 mph.