A storage vessel is well stirred and contains $500kg$ of total solution with a concentration of $5\mathrm{.}0\%$ salt. A constant flow rate of $900k\frac{g}{h}$ of salt solution containing $16\mathrm{.}67\%$ salt is suddenly introduced into the tank and a constant withdrawal rate of $600k\frac{g}{h}$ is also started. These two flows remain constant thereafter. Derive an equation relating the outlet withdrawal concentration as a function of time. Also, calculate the concentration after $2\mathrm{.}0h.$