A mixture of benzene and toluene containing 60 mole percent benzene is to be separated into an overhead product containing 96 mole percent benzene and a bottoms containing 25 mole percent benzene. A valve-tray tower has been designed which is intended to accomplish this separation at atmospheric pressure. At the operating conditions chosen, calculations have shown that 6.1 theoretical stages are necessary. The temperature is 181°F at the top of the column and 213°F in the reboiler. Assuming the reboiler acts as one theoretical stage, estimate the number of actual trays required. Benzene and toluene mixtures may be considered as ideal. At 197°F, the vapor pressure of pure benzene is 1070 mm Hg and the vapor pressure of pure toluene is 429 mm Hg.