Acetone is to be extracted from a solution in water, using 1,1,2-trichloroethane. The feed concentration is 45.0% w/w acetone. Determine the number of stages required to reduce the concentration of acetone to below 10%, using 32 kg of extraction-solvent per 100 kg feed. The equilibrium data for this system are given by Treybal, Weber, and Daley (1946).