A long slope is formed in a soil with shear strength parameters: c’ = 0 and φ’ = 34^o. A firm stratum lies below the slope and it is assumed that the water table may occasionally rise to the surface, with seepage taking place parallel to the slope. Use γ_sat = 18 kN/m³ and γ_w = 10 kN/m³. The maximum slope angle (in degrees) to ensure a factor of safety of 1.5, assuming a potential failure surface parallel to the slope, would be