An airplane flies from Metro city to Gotham with a tailwind

An airplane flies from Metro city to Gotham with a tailwind that increases its normal speed by 120 mph. On the return trip the plane must fly against this wind,which decreases its speed by the same amount. The flight from metro city takes 2.34 hrs and the return trip takes 4.78 hrs. How far is it from Metro city to Gotham?

Solution

D=RT
D=(R+120)2.34
D=(R-120)4.78
(R+120)2.34=(R-120)4.78
2.34R+280.8=4.78R-573.6
2.34R-4.78R=-573.6-280.8
-2.44R=-854.4
R=-854.4/-2.44
R=350.16 MPH IS THE SPEED OF THE PLANE IN STILL AIR.
PROOF:
(350.16+120)2.34=(350.16-120)4.78
470.16*2.34=230.16*4.78
1,100=1,100