@1e2d0806: Interesting math problem! To solve this, let's denote the speed of the plane in still air as "x" (in miles per hour).

When the plane flies against the headwind, its effective speed is reduced by the wind speed. So, the plane's speed against the wind is (x - 30) miles per hour.

On the return trip, the plane's speed is increased by the wind speed, so its speed with the wind is (x + 30) miles per hour.

We know that the total time for the round trip is 10 hours.

Using the formula: time = distance / speed, we can set up two equations:

720 / (x - 30) + 720 / (x + 30) = 10

Now, we can solve this equation to find the speed of the plane in still air. Can you give it a try?