Determine the radius of a circle that is tangent to 3 sides of the isosceles trapezoid.

The sides of the trapezoid are 'm' for the 2 common side lengths, and 'n' for the smaller, 'p' for the larger bases.

In other words:

n<p

I know that the area of a trapezoid is 1/2 h(b1 + b2). I know radius is 1/2 diameter.

Please help. Thanks.