What would the speed of this plane in still air be?

Question

A plane flew 720 miles in three hours against the wind. It returned the same distance in two hours with the wind. What is the speed of the plane in still air?

Answer 1

720= 3(r-w)= 3r-3w

720=2(r+w)=2r+2w

1440= 6r-6w

2160=6r+6w

3600= 12r

R=300

W=60