4. A distillation column with a total condenser and a partial reboiler is separating an ethanol-water mixture at a pressure of 1 atmosphere. The feed is a saturated liquid that is 25 mole \% ethanol and the feed rate is 800moles/hr. A bottoms composition of 5 mole \% ethanol is desired. The reflux is returned as a saturated liquid and constant molal overflow can be assumed. Find the minimum reflux ratio and the number of stages required at total reflux (minimum number of stages) if the distillate composition is: a. 70 mole \% ethanol b. 85 mole % ethanol