Electrostatics - force on point charges by electric field

[risk2112]

Homework Statement

A square, with each corner as a point charge, A, B, C, and D. They all have the same charge of 5.0 x 10 ^(-6) C. Length of each side of the square is 0.1 m. 2 negative charges diagonal from each other, and the other two are positive, diagonal from each other.
Question asks net force on each point charges and electric field and electric potential at centre of the square.
A, B, C, D = 5.0 x 10^(-6) C
radius = 0.1 m
2 negative charges diagonal
2 positive charges diagonal
Square of four corners A, B, C, D.

Homework Equations

F_e = kq1q2/r^2
F_e = qE
idk equation for electric potential

The Attempt at a Solution

For each net force, are they all the same except with opposite directions? Like say 5 N NW, 5 SW, 5 SE, 5 NE. If so, then I can figure out that part.
I really have no idea for the electric potential or electric field, but I am guessing one of the two is going to have either an electric potential of 0 or electric field of 0. I don't know how to solve for either of them though.

 

[risk2112]

I calculated the force, being 9.1 x 10^(something, forgot) N, but I don't know how to use F_e for the middle, with a charge in the middle as q...in order to get E (electric field) for middle. Also, is the E for electric field what makes V (electric potential) = radius x electric field?