Which could be the first step in solving the equation represented by the model below?

A. Add 4 negative unit tiles to both sides.
B. Add 4 negative unit tiles to the left side, and add 6 negative unit tiles to the right side.
C. Add 4 positive unit tiles to both sides.
D. Add 6 negative unit tiles to the left side, and add 4 negative unit tiles to the right side.