One Point Charge $+ Q$ Is Placed at the Center of a Square, and a of a Square

One point charge $+ Q$ is placed at the center of a square, and a second point charge $- Q$ is placed at the upper-left corner of the square. It is observed that an electrostatic force of magnitude $2.0 \mathrm {~N}$ acts on the positive charge at the center. Now a third charge $- Q$ is placed at the lower-left corner of the square, as shown in the figure. What is the magnitude of the net force that acts on the center charge now?

A) $4.0 \mathrm {~N}$
B) $0.0 \mathrm {~N}$
C) $5.3 \mathrm {~N}$
D) $2.8 \mathrm {~N}$