The drawing shows an equilateral triangle, each side of which has a length of 2.12 cm. Point charges are fixed to each corner, as shown. The 4.00 $\mu$C charge experiences a net force due to the charges $q_A$ and $q_B$. This net force points vertically downward and has a magnitude of 666 N. Determine the charge $q_A$, in microCoulombs, $\mu$C.
+4.00 $\mu$C