2006 Gauss 8 Problem 12

In the diagram, what is the area of the shaded triangle?

\textbf{(A)}\ 6.5 \text{ cm}^2\quad \textbf{(B)}\ 7.5 \text{ cm}^2\quad \textbf{(C)}\ 15 \text{ cm}^2\quad \textbf{(D)}\ 13 \text{ cm}^2\quad \textbf{(E)}\ 22.5 \text{ cm}^2

If there are no answer choices shown, enter a numerical answer.

Full credit to this problem is given to the CEMC, you may view all Gauss contests here.