申論題

1. Suppose that we have a system (showing in Figure 1) consisting of two interconnected tanks, each containing a brine solution. Tank A contains x(t) pounds of salt in 200 gallons of brine, and tank B contains y(t) pounds of salt in 300 gallons of brine. The mixture in each tank is kept uniform by constant stiring. When t = 0, brine is pumped from tank A to tanks B at 20 gallons/minute and from tank B to tank A at 20 gallons/minute. If x(0) = 10 and y(0) = 40.