Two infinite, parallel, charged planes have charge per unit area σ1 = +3σ and σ2 = –σ, res...

Two infinite, parallel, charged planes have charge per unit area σ1 = +3σ and σ2 = –σ, respectively, with σ > 0 (Fig. P17.78). What are the magnitude and direction of the electric field at points A, B, and C?

Figure P17.78