A 3-ft depth of stagnant water at 25oC lies on top of a 0.10-in. thickness of NaCl. At time < 0, the water is pure. At time = 0, the salt begins to dissolve and diffuse into the water. If the concentration of salt in the water at the solid-liquid interface is maintained at saturation (36 g NaCl/100 g H20) and the diffusivity of NaCl in water is 1.2 x 10–5 cm2/s, independent of concentration, estimate, by assuming the water to act as a semi-infinite medium, the time and the concentration profile of salt in the water when

(a) 10% of the salt has dissolved

(b) 50% of the salt has dissolved

(c) 90% of the salt has dissolved