Two balls carrying charges $+7\mu C$ and $-5\mu C$ attract each other with a force $F$. If a charge $-2\mu C$ is added to both, the force between them will be:

$\left(\frac{1}{4{\mathrm{\pi \epsilon }}_0}=9\times {10}^9 \mathrm{N} {\mathrm{m}}^2 {\mathrm{C}}^{-2}\right)$

A point charge $q_1$ exerts a force $F$ upon another point charge $q_2$. If a third charge $q_3$ be placed quite close to the charge $q_2$, then the force that charge $q_1$ exerts on the charge $q_2$ will be,