16. The base of a solid \( S \) is the semicircular region enclosed by the graph of \( y = \sqrt{9 - x^2} \) and the x-axis. If the cross sections of \( S \) perpendicular to the x-axis are semicircles, what is the volume of the solid?
Answer is: option3
Solution:
\( \frac{9\pi}{2} \)
