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