2018 Cayley Problem 2

In the diagram, 3 of the 1 \times 1 squares that make up the 4 \times 5 grid are shaded. How many additional 1 \times 1 squares need to be shaded so that one-half of all of the 1 \times 1 squares are shaded?

\textbf{(A)}\ 5\quad \textbf{(B)}\ 9\quad \textbf{(C)}\ 7\quad \textbf{(D)}\ 6\quad \textbf{(E)}\ 8

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 Cayley contests here.