i think that's two semicircles...one with a radius of 2 and one with a radius of 4. Subtracting the area of the one with radius 2 from the one with radius 4 would give you the answer
Area = (area of larger semicircle)-(area of smaller semicircle)
= [tex] \frac{1}{2} \pi (4)^2 - \frac{1}{2} \pi (2)^2 [/tex]
= [tex]6 \pi [/tex]
