Streptomycin is extracted from the fermentation broth using an organic solvent in a counter-current staged extraction unit. The distribution coefficient of streptomycin at pH = 4 is KD = Yi/Xi = 40, and the flow rate of the aqueous (H) phase is H= 150 L/min. If only five extraction units are available to reduce the streptomycin concentration from 10 g/L in the aqueous phase to 0.2 g/L, determine the required flow rate of the organic phase (L) in the extraction unit.