Taking into account the Coulomb's Law: [tex]F_e = K\cdot \frac{Q_1\cdot Q_2}{d^2}[/tex]
If the value of "d" is tripled:
[tex]F_e = K\cdot \frac{2Q_1\cdot Q_2}{(3d)^2} = K\cdot \frac{Q_1\cdot Q_2}{9d^2} =\bf \frac{F_e}{9}[/tex]
The new force is nine times smaller.