Velocity with wind = 1,980 / 4.5 = 440 mph Velocity against wind =1,980 / 5.5 = 360 mph Plane in still air - wind speed = 360 Plane in still air + wind speed =440 Adding both equations: 2*Plane in still air = 800 Plane in still air = 400 mph Plane in still air + wind speed =440 Therefore, wind speed = 40 mph