A tank initially contains 108 liters of pure water. Brine containing 3 lb salt/liter begins to enter the tank at a rate of 1 liter/min and the well-mixed solution is drained at 2 liters/min. How much salt is in the solution after 10 minutes? () To obtain an equation for the salt in the solution (in pounds), note that we can determine the rate of change of the amount of salt in the tank at time t by finding the difference between the rate at which the salt enters the tank and the rate at which the salt exits the tank (rate in rate out). The amount in can be computed by multiplying (concentration of brine in) (flow rate of brine in), How do we get an equivalent function for the rate at which the salt in the solution leaves the tank? Why must we know the volume of the solution in the tank