2014 Fermat Problem 18

A square is cut along a diagonal and reassembled to form the parallelogram PQRS as shown in the diagram. If PR = 90 mm, what is the area of the original square, in \text{mm}^2?

\textbf{(A)}\ 324\quad \textbf{(B)}\ 1620\quad \textbf{(C)}\ 1800\quad \textbf{(D)}\ 2025\quad \textbf{(E)}\ 2700

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