Question 858953
let speed with no wind be x 
and speed of wind be y

40/2.5=16.5
x+y=16.5
20/1.7=11.8
x-y=11.8

add the equations

2x=28.3 
x= 14.15 yards/s -speed in still air

speed of wind = 16.5-14.15 = 2.35yards/s