Question 388500
The key to most of these types of problems is to determine an equality.  In this case, the equality is the speed of the plane in still air.

speed of plane downwind = 1200/2 = 600 mi/h
speed of plane against the wind =1200/2.5=480 mi/hr

downwind speed - wind speed = against the wind speed + wind speed
let x = wind speed
600-x=480+x
2x=120
x=60
ans: wind speed is 60 mi/hr