Two charges of  3 C  and  2 C are positioned on a line at points  6  and  4 , respectively. What is the net force on a charge of  3 C at  2 ?

The electrostatic force $F$ between two point charges ${Q}_{1}$ & ${Q}_{2}$ separated by a distance $D$ is given by the following formula
$F = \setminus \frac{1}{4 \setminus \pi \setminus {\epsilon}_{o}} \setminus \frac{{Q}_{1} {Q}_{2}}{{D}^{2}}$