Exercise 106

Suppose the tanks are as in an example in the source text except that clean water flows in at a rate of $s$ liters per second into tank 1, and brine flows out of tank 2 and into the sewer also at a rate of $s$ liters per second. The rate of flow from tank 1 into tank 2 is still $r$, but the rate of flow from tank 2 back into tank 1 is $r-s$ (assume $r > s$).

1. Draw the picture.
2. Set up the system of equations.
3. Intuitively, what happens as $t$ goes to infinity, explain.