A light private plane can fly 120 mph in still air Flying ag

A light private plane can fly 120 mph in still air. Flying against the wind, the plane can fly 320 miles in the same time it requires to fly 640 miles with the wind. Find the rate of the wind.

Solution

D=RT OR T=D/R
T=320/(120-W)
T=640/(120+W)
320/(120-W)=640/(120+W)
640(120-W)=320(120+W)
76,800-640W=38,400+320W
-640W-320W=38,400-76,800
-980W=-38,400
W=-38,400/-960
W=40 MPH IS THE WIND SPEED.
PROOF:
320/(120-40)=640/(120+40)
320/80=640/160
4=4