A soil profile consists of 10 m of sand over 10 m of clay over rock as shown in the attached figure. The water table is at 5 m below the ground surface. For sand, Gs = 2.65, e = 0.58, and the degree of saturation above the water table is 60%. For clay, Gs = 2.70, e = 0.54. What is the vertical effective stress at 17 m below the ground surface? (Gs = specific gravity, e = void ratio)