short cut method!

how do i know how many stages do i need?

Design a distillation column to perform the separation of 9,250kg/hr of a 55wt% benzene and 45 wt%2,2,4 trimethylpentane mixture. The column feed consists of 60% vapor at 2 bar. The column must recover 99.9% of benzene in the overhead and 91.0% of 2,2,4 trimethylpentane from the column base. The column condenser operates at 2.0 bar. Assume a pressure drop per tray of 0.008 bar. Select an appropriate method for computing properties. 1) Use a short-cut method to: a. Identify the light and heavy key components. b. Investigate the effect of reflux ratio on the number of theoretical stages. c. Select the optimum reflux ratio. d. Determine the number of stages at this reflux ratio. e. Estimate the feed point