On a plane within a saturated soil mass, the total normal stress is 185 kPa, the pore-water pressure is 98 kPa and the shear stress is 42 kPa. The soil undergoes shear failure and reaches critical state on this plane when the pore-water pressure is increased to 120 kPa while keeping the total normal and shear stresses constant. What is the critical state angle of friction of the soil?