Think of it in terms of the entire circle. A semi-circle is just half a circle, so the area of a semicircle will be half of the area of the entire circle. The radius of the semicircle is 6, so the radius of the whole circle is 12. Then, we can do [tex]\frac{pi*r^{2} }{2}[/tex] to get the area of the semicircle is 72π. I'm pretty sure that's right. Let me know if I made a mistake somewhere.
