Question 22294
Let "p" be the speed of the plane in still air.

With the wind:
  distance = 720    rate = p+30
Therefore time = 720/(p+30)

Against the wind:
  distance = 720   rate = p-30
Therefore time = 720/(p-30)

Equation:
   Time with + Time against = 10
   720/(p+30) + 720/(p-30) = 10

Solve for "p" to get the answer you need.

Cheers,
Stan H.