2018 Pascal Problem 6

In the diagram, 18 identical 1 \times 2 rectangles are put together to form a 6 \times 6 square. Part of the square is shaded, as shown. What percentage of the area of the 6 \times 6 square is shaded?

\textbf{(A)}\ 50\%\quad \textbf{(B)}\ 67\%\quad \textbf{(C)}\ 75\%\quad \textbf{(D)}\ 33\%\quad \textbf{(E)}\ 25\%

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.