How do you know the direction of the Field due to a charge with nonconducting sheets with uniform charge densities?

Hi, I've been doing my homework and I'm still unsure with the directions of my electric field. Here's the link of the details:

http://imgur.com/sM9XFkQ http://imgur.com/a/1Ogoq

Because it is an "infinite" nonconducting sheet we use E= σ/2ϵo then we sum up all the E due to charge 1-4. I get that part, but the thing I don't get is that at Point A we'll have to do ΣE= -E1-E2-E3-E4

Why would it be all negative? Thanks so much!