The Number of Golf Balls Ordered by Customers of a Pro

Multiple Choice

The number of golf balls ordered by customers of a pro shop has the following probability distribution. $\begin{array}{|c|c|}\hline \mathrm{x} & \mathrm{P}(\mathrm{x}) \\\hline 3 & 0.14 \\6 & 0.29 \\9 & 0.36 \\12 & 0.11 \\15 & 0.10 \\\hline\end{array}$

A) $\mu = 8.22$
B) $\mu = 9$
C) $\mu = 9.3$
D) $\mu = 5.55$