A plane travels 1200 km distance in 12 hrs with the wind The

A plane travels 1200 km distance in 12 hrs with the wind. The return trip against the wind takes 15 hrs. Find the rate of the plane in still air.

D=RT OR R=D/T
R=1200/12
R=100 MPH. IS THE SPEED WITH THE WIND
R=1200/15
R=80 MPH IS THE SPEED AGAINST THE WIND.
(100+80)/2=180/2=90 MPH IS THE SPEED OF THE PLANE IN STILL AIR.