(1) Setup but do not solve the initial value problem necessary to solve the following problem. A 100 gallon tank contains 80 gallons of pure water. A brine solution with 4 lb/gal of salt enters the tank at 3 gal/min, and the well-mixed solution leaves at the rate of 2 gal/min. How much salt is in the tank when the tank fills completely? Be sure to indicate what you are to solve for but do not compute the numerical value