Finely shredded waxed paper is fed to a continuous countercurrent extraction system at the rate of 40 kg/hr. Since wax is infinitely soluble in kerosene, the paper is to be de-waxed using kerosene The waxed paper contains 20 weight% wax, and the remaining paper is insoluble in kerosene and forms a slurry. After extraction, the slurry must not contain more than 3 kg of wax per 100 kg of dry, wax-free paper. The kerosene that is fed into the extraction battery is not pure and contains 0.05 kg of wax per 100 kg of liquid. After the leaching step, the paper slurry retains 3 kg of liquid for every kg of liquid free pulp. The extract from the battery is to contain 7 kg wax per 100 kg of liquid .

After the leaching step, you may assume that underflow and overflow are constant.

 how many ideal stages are required?