4. A saturated liquid mixture containing 60mole% benzene and 40 mole % toluene is to be distilled into a distillate product containing 90mole% benzene and the bottom product containing 5 mole % benzene. The fractional distillation column will operate at approximately constant pressure of 1atm. The reflux ratio is 2 . How many theoretical plates will be there in the column? Equilibrium data