We need to find the radius of the circle....so we have that

8 pi = 2pi * r divide both sides by 2pi

4 cm = r

(1/3) of the area of this triangle can be found as :

(1/2) r^2 sin (120° ) =

(1/2) 4^2 * √3/2 =

4√3 cm^2

So....3 times this is just

12√3 cm^2 ≈ 20.78 cm^2