A plane takeoff at  PM.

The plane travels a distance of  miles in  hours.

The average velocity is .

The Rolles theorem can be applied because the function involved in the flight is continuous on the interval  and differentiable on the interval .

So, there exist a number  in the interval  such that .

 and  is maximum value of .

The plane should cross  miles per hour while take off and landing off.

The plane follows the concave down parabola form so the plane must cross the two times when its speed is  miles per hour.