Consider a closed system of three well-mixed brine tanks. Tank 1 has volume 20 gallons, tank 2 has volume 15 gallons, and tank 3 has volume 4 gallons. Mixed brine flows from tank 1 to tank 2, from tank 2 to tank 3, and from tank 3 back to tank 1. The flow rate between each pair of tanks is 60 gallons per minute. At time zero, tank 1 contains 28 lb of salt, tank 2 contains 11 lb of salt, and tank 3 contain no salt. Solve for the amount (lb) of salt in each tank at time t (minutes). Also determine the limiting amount (as t→∞) of salt in each tank. (Solve the problem by using Eigenvalues and Laplace Transform)