Question

The magnitude of the charges is |q| = 7.8 µC, and the distance between them is d = 2.7 mm.
Charge 2 is attracted to charge 1, because they are opposite charges. Charge 2 is repelled from charge 3, because they are like charges. Therefore, both 21 and 23 point to the left.
F=?

I have no idea what the geometric arrangement is, however, add the forces as vectors.