Which way does electric field line go?

[cashflow]

Homework Statement

Given symmetrically placed rectangular insulators with uniformly charged distributions of equal magnitude as shown in the figures be low, find the net electric field at the origin.
[PLAIN]http://img254.imageshack.us/img254/8684/electricf.jpg
In the figure above, at the origin, the net field E_net is
1. aligned with the positive y-axis.
[STRIKE]2. non-zero and is not aligned with either the x- or y-axis.[/STRIKE]
[STRIKE]3. zero and the direction is undefined.[/STRIKE]
4. aligned with the positive x-axis.
5. aligned with the negative x-axis.
6. aligned with the negative y-axis.

2 and 3 were wrong.

Homework Equations

None?

The Attempt at a Solution

I think they are asking for the direction of the electric field. Actually, I have no idea what I am supposed to solve for. I know I have to find Enet but how? Thanks in advance!

 

[cashflow]

I'm sorry for the double post. The answer to the above is 5 (aligned with the negative x-axis). I was on the right track, since the field lines travel towards the negatively charged rectangle. But I'm still not sure for the other 4 I'm supposed to solve for. Do I just figure out the direction of field lines? Thank you.

EDIT: Yes, I was right. Just find the direction of the field lines at (0,0). It seems I have answered my own question :)