In the diagram, a sector of a circle has central angle $120^{\circ}$. The area of the whole circle is $9 \pi$. What is the area of this sector?
(A) $2 \pi$
(B) $3 \pi$
(C) $4 \pi$
(D) $6 \pi$
(E) $\frac{9}{2} \pi$

![](https://cdn.mathpix.com/cropped/2024_04_20_e85ef69091c57cb633f3g-032.jpg?height=385&width=380&top_left_y=1491&top_left_x=1293)
The entire central angle in a circle measures $360^{\circ}$.

In the diagram, the central angle which measures $120^{\circ}$ represents $\frac{120^{\circ}}{360^{\circ}}=\frac{1}{3}$ of the entire central angle.

Therefore, the area of the sector is $\frac{1}{3}$ of the area of the entire circle, or $\frac{1}{3} \times 9 \pi=3 \pi$.

ANSWER: (B)