Answer
$F = 8990 N \approx 9.0 \times 10^3 N$
Work Step by Step
We know that $Q = 6.0 \times 10^{-6} C$. When Q is divided into two equal charges, it becomes $Q/2$. From Coulomb's Law,
$F = \frac{Q^2}{4\pi \epsilon_o r^2}$
$F = \frac{(\frac{Q}{2})^2}{4\pi \epsilon_o r^2}$
$F = \frac{(\frac{Q^2}{4})}{4\pi \epsilon_o r^2}$
$F = \frac{Q^2}{(4)4\pi \epsilon_o r^2}$
Where $\frac{1}{4\pi \epsilon_o} = 8.99 \times 10^{9} N.m^2/C^2$,
$Q = 6.0 \times 10^{-6} C$.
$r = 3.0 \times 10^{-3}m$
$F = \frac{(6.0 \times 10^{-6} C)^2}{(4)(8.99 \times 10^{9} N.m^2/C^2) (3.0 \times 10^{-3}m)^2}$
$F = 8990 N \approx 9.0 \times 10^3 N$
