A saturated liquid mixture of 0.4 mole fraction n-hexane and 0.6 mole fraction n-octane is fed at a rate of 100 moles/h to a distillation column. The column contains a total condenser and a regular reboiler. The reflux ratio at the top of the column is 0.5. The distillate product is 0.95 mole fraction n-hexane, and the mole fraction of n-hexane in the stream from the reboiler is 0.05. A cooling coil is submerged in the liquid of the second plate from the top of the column. The coil removes sufficient heat to condense 50 mol % of the vapor rising from plate 3. Constant molal overflow can be assumed. Determine the number of plates required and the location of the feed plate.