2006 Pascal Problem 12

The lengths of the three sides of a triangle are 7, x+4 and 2x+1. The perimeter of the triangle is 36. What is the length of the longest side of the triangle?

\textbf{(A)}\ 7\quad \textbf{(B)}\ 12\quad \textbf{(C)}\ 17\quad \textbf{(D)}\ 15\quad \textbf{(E)}\ 16

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 Pascal contests here.