Given two charges, [tex] Q_{1}[/tex] and [tex]Q_{2}[/tex], we can calculate for the electric force with
[tex] Force = \frac {k Q_{1} Q_{2}}{r^{2}}[/tex]
with k as the Coloumb constant and r as the distance given to be 3 cm or 0.03 m. Plugging this in, we have
[tex]F = \frac{(9.0 x 10^{9})(10^{-6})(10^{-6})}{0.03^{2}}[/tex]
Thus, we have F = 10 N.
Answer: 10N