An extraction column is used to remove an impurity P from toluene with water as the solvent. The toluene and water may be considered to be completely immiscible. The toluene enters the column with 20 wt% P and it should leave with 1.0 wt% P. The water used as solvent enters the column as pure water. Feed flow rate is 200 lb/hr. Solvent rate is 300 lb/hr. Find the number of equilibrium stages required. Over the required range of operation equilibrium data can be satisfactorily represented as: wt frac P in water = 0.75 (wt frac P in toluene) + 10.0 (wt frac P in toluene)