Solution to task 321 from Chertov's for extramural stud

321. On two concentric spheres of radius R and 2R, charges with surface densities σ1 and σ2 are evenly distributed (Fig. 24). It is required: 1) using the Ostrogradsky-Gauss theorem, find the dependence E (r) of the electric field strength on the distance for three regions: I, II and III. Take σ1 = 4σ, σ2 = σ; 2) calculate the intensity E at a point remote from the center at a distance r, and indicate the direction of the vector E. Take σ = 30 nC / m2, r = 1.5R; 3) build a graph of E (r).