You can put this solution on YOUR website!
The radius is the distance between the two points given.
They have the same y coordinate, so the distance is the difference between the x coordinates
A circle is the collection of all the points at a certain distance from the center point.
Your circle is the collection of all the points at a distance of 15 from the center point (-6, 4).
The distance squared would be
The square of the distance from a point (x, y) to (-6, 4) is
If that point is in the circle of the problem,
That equation is the equation of the circle with center (-6,4) passing through the points (9,4). If a point is in that circle its coordinates will satisfy that equation. If the coordinates of a point satisfy that equation, the point is in the circle.