2. A soluble solid in an ore must be leached with water in a continuous counter current extraction cascade. 100 kg of the ore containing 8% solute, 12% moisture and 80% inert material must be treated per an hour. The final extract solution must contain 18% solute and must be free from solid material. 95% of the solute in the ore must be extracted. The underflow is constant throughout containing 1.7 kg water/ kg inert material. Determine the number of equilibrium washing stages required