325. Charges with surface densities σ1 and σ2 are uniformly distributed on two infinite parallel planes (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 = 2σ, σ2 = σ; 2) calculate the field strength E at a point located to the left of the planes, and indicate the direction of the vector E; 3) build a graph of E (x).