Question 70489
let statements:
let x be the be speed of the plane in still air.
Let y be the speed of the wind.
since d=rt, we can come upwith a system of equations. 
625=2.5(x+y)
625=4 1/6(x-y)
The first equation could be simplied into 250=x+y.
the second equation, multiply both sides to the reciprocal of 4 1/6, which is 6/25:
150=x-y
now, line them up, and use addition method.
x-y=150
x+y=250
2x=400
x=200
Plug this value back for y. 200-y=150, y=50. 
The speed of the plane in still is 200 m/h, whhile the speed of the wind is 50 m/h.