Problem $3.$

For a four$-$stage solvent extraction process, calculate the concentration of metal in the organic phase in the fourth stage given that the flow rate of aqueous solution is $1000\frac{\text{I}}{m}in,$ the organic flow rate is $500\frac{\text{I}}{m}in,$ the aqueous feed concentration is $6\frac{g}{l},$ the aqueous raffinate solution concentration is $0\mathrm{.}1\frac{g}{l},$ and the initial concentration of metal in the organic feed solution is $0\mathrm{.}5\frac{g}{1}.$