A counter-current extraction column is designed to remove 99% of solute C from a solution of solvent A and solute C using pure solvent B. The initial concentration of solute in the solution of A + C is 20 wt %, and the total flow of solution is 1000 kg/h. If the equilibrium relationship is Y = 2X , where Y = mass of C/mass of A and X = mass of C/mass of B.T he minimum flow rate of solvent B required (in kg/h) is
