327. On two infinite parallel planes, charges with surface densities σ1 and σ2 are uniformly distributed (Fig. 25). It is required: 1) using the Ostrogradsky-Gauss theorem and the principle of superposition of electric fields, find the expression E (x) of the electric field strength in three areas: I, II and III. Take σ1 = σ, σ2 = -2σ; 2) calculate the field strength E at the point located to the right of the planes, and indicate the direction of the vector E, σ = 20 nC / m2; 3) build a graph of E (x).