2005 Pascal Problem 22

In the diagram, two pairs of identical isosceles triangles are cut off of square ABCD, leaving rectangle PQRS. The total area cut off is 200 m^2. The length of PR, in metres, is

\textbf{(A)}\ \sqrt{200}\quad \textbf{(B)}\ 20\quad \textbf{(C)}\ \sqrt{800}\quad \textbf{(D)}\ 25\quad \textbf{(E)}\ 15

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.