In the counter-flow tower, it is desired to extract ethanol from the ethanol-air mixture with water. It is aimed for 80% of the ethanol in the air-ethanol mixture to pass into water. The air-ethanol mixture is fed to the tower at 100 kg mol/h. Pure water supplied to the tower as liquid phase enters in the amount of 300 kg mol/h. The system operates under 101.3 Kpa pressure at 300K temperature. The equilibrium relationship between gas and liquid phases of ethanol is given as Ya = 1.25 Xa. Determine the number of stages theoretically required to complete the separation process.