Two solutions, feed F at the rate of 7,500 kg/h containing 50 wt% acetone and 50 wt% water, and feed F' at the rate of 7,500 kg/h containing 25 wt% acetone and 75 wt% water, are to be extracted in a countercurrent system with 5,000 kg/h of 1, 1, 2-trichloroethane at 25°C to give a raffinate containing 10 wt% acetone. Calculate the number of equilibrium stages required and the stage to which each feed should be introduced, using a right-triangle diagram. Equilibrium data are given in Exercise 8.11.