In the two tanks shown in the figure below, there are 1000 L of pure water and 1000 L of solution at a concentration of 0.2 kg of salt/L, respectively. In order to equalize the salt concentration in both tanks, the solution is pumped from the tanks to each other at a flow rate of 50 L/min. Derive expressions that relate the concentration in the tanks to time. Find the time required for the concentrations to equalize.