A mixture of 60,30 , and 10 mole percent benzene, toluene, and xylene respectively is separated by a platecolumn to give a top product containing at least 90 mole per cent benzene and a negligible amount of xylene, and a waste containing not more than 60 mole per cent toluene. Using a reflux ratio of 4 , and assuming that the feed is boiling liquid, determine the number of plates required in the column, and the approximate position of the feed plate. The relative volatility of benzene to toluene is 2.4 and of xylene to toluene is 0.45 , and it may be assumed that values are constant throughout the column