Electric field at center between two charged 12 cm disks

[skli]

I have a homework problem which is about the electric fields of disks. I have spent so much time on it, but still can't get the right answer. Please help :)
Two 12.0-cm-diameter charged disks face each other, 25.0cm apart. Both disks are charged to - 70.0nC . What is the electric field strength at the center of the left disk?

 

[mjsd]

you mention that you have spent so much time on this. maybe you can show us how you started this problem. that way it is easier for us to spot where you are having trouble with.
cheers