Aparabola intersects the x-axis at x = 3 and x = 9.
what is the x-coordinate of the parabola's vertex?

The x-coordinate of the parabola's vertex is 6.

Step-by-step explanation:

A parabola in the following format:

With

Has the following vertex:

In which

In this problem, we have that:

A parabola intersects the x-axis at x = 3 and x = 9. This means that the roots are x = 3 and x = 9, and that our parabola is defined by the following equation:

So

The x-coordinate of the parabola's vertex is 6.