Calculating Net Electrostatic Force in a Square Configuration

[name_ask17]

Homework Statement

There are four charges, each with a magnitude of 2.1 µC. Two are positive and two are negative. The charges are fixed to the corners of a 0.25 m square, one to a corner, in such a way that the net force on any charge is directed toward the center of the square. Find the magnitude of the net electrostatic force experienced by any charge.

Homework Equations

f=kQq/d^2

The Attempt at a Solution

can you start me off on this prob? i honestly don't know how to do it.

 

[dangish]

You could get the x and y component of each charge on the centre, that's a start

 

[name_ask17]

ok. so i get the attractive force as root(2)kq^2/d^2
and after that I am stuck