In the salted stage, a piece of cheese slab with a thickness of 15 cm is introduced in a brine bath that possesses a salt concentration of 131 kg/m3 . The concentration at the surface immediately attains a value of 131 kg NaCl/m3 and remains constant during the brining process. The cheese did not contain any salt at the beginning. The diffusion coefficient for NaCl in the cheese is 9.6x10-9 m2 /s, while the mass transfer coefficient in the liquid phase has a value of 2x10-5 m/s. Calculate the salt concentration in the center of the cheese piece after 2 days.