For the original distance, the plane flew at its speed (x) minus 60 MPH (the plane is traveling against the headwind, so the headwind subtracts from the plane's speed). D = (x-60) * 5
For the return trip the tailwind adds to the speed. The round trip was 9 hours, and the original trip took 5 hours, so the return trip took 9-5 = 4 hours. D = (x+60) * 4
Those distances are equal. (x-60)*5 = (x+60)*4
5x - 300 = 4x + 240
x = 540 MPH
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