1. The problem statement, all variables and given/known data The three parallel planes of charge shown in the figure have surface charge densities (-1/2)η, η, and (-1/2)η. 2. Relevant equations I think that the electric field is equal to eta divided by epsilon naught. 3. The attempt at a solution Well, I know that the electric field at regions 1 and 4 are zero. E1 = E4 = (-1/2)η + η + (-1/2)η = 0. I know that the electric field in region 2 points upward and that the electric field at region 3 points downward. However, I am not sure how to calculate the electric field in these regions. How do I go about calculating the electric field in these regions?