A continuous fractionating column operating at atmospheric pressure is to separate a feed containing 30% CS2 and 70% CCl4 into an overhead product of 95 % CS2 and a bottom product of 95 mole % CCl4. The feed enters as saturated mixture with 50% vapor. Assuming an overall plate efficiency of 70% and a reflux ratio of 3:1, estimate the number of plates needed. All the compositions are in mole %. Assume a constant relative volatility of 2.7. A total condenser and an internal reboiler are used.