Tank initially contains gal of water and oz of salt, and Tank initially contains gal of water and oz of salt. Water containing oz/gal of salt flows into Tank at a rate of gal/min. The mixture flows from Tank to Tank at a rate of gal/min. Water containing oz/gal of salt also flows into Tank at a rate of gal/min (from the outside). The mixture drains from Tank at a rate of gal/min, of which some flows back into Tank at a rate of gal/min, while the remainder leaves the system. Let and , respectively, be the amount of salt in each tank at time . Write down differential equations and initial conditions that model the flow process. Observe that the system of differential equations is nonhomogeneous. Find the values of and for which the system is in equilibrium, that is, does not change with time. Let and be the equilibrium