Hello,Originally Posted byYumi

I've attached a diagram to demonstrate what I calculated.

Let r be the radius of the circle.

Let angle(CBA)= alpha. Then angle(DCB)=180°-alpha.

The triangle (BMO) is a right triangle. The triangle (OSC) is a right triangle.

Now use the tangens:

with

So you get:

Solve for r and you'll get r = 6.

That means the height of the trapezoid is 12. Therefore the area is 156 (square units).

Greetings

EB