Find the dielectric constant of the medium?

[pwn2d2]

Homework Statement

Two point charges a distance d apart in free space exert a force of 1.4∗10^−4 [N]. When the free space is replaced by a homogeneous dielectric medium, the force become .9∗10^−4 [N]. What is the dielectric constant ϵr of the medium?

Homework Equations

E=F/Q

The Attempt at a Solution

I have been staring at this problem for awhile. I can only think of using E=F/Q. But the problem is this only applies to free space and I do not know Q. So I am not sure where to start to compare the free space and medium.

 

[sbhit2001]

The coulombic force in free space is k.q1.q2/r^2. In a medium, the value of k changes to k/dielectric constant. Now try to solve the question. :D
Hint : Compare the 2 values of electrostatic force.