Fresh water is to be obtained from brackish water at 65oF with a salinity of 0.12 percent

Question:

Fresh water is to be obtained from brackish water at 65oF with a salinity of 0.12 percent on mass basis (or TDS = 1200 ppm). Determine
(a) The mole fractions of the water and the salts in the brackish water,
(b) The minimum work input required to separate 1 lbm of brackish water completely into pure water and pure salts, and
(c) The minimum work input required to obtain 1 lbm of fresh water.