A stratum of clay is 2 m thick and has an initial overburden pressure of 50 kN/m' at the middle of the clay layer. The clay is overconsolidated with a preconsolidation pressure of 75 kN/m². The values of the coefficients of recompression and compression indices are 0.05 and 0.25 respectively. Assume the initial void ratio e=1.40. Determine the final settlement due to an increase of pressure of 40 kN/m² at the middle of the clay layer.