A large tank with capacity of 100 gallons haves 50 gallons of pure water. A salt solution with oncentration of 0.1 lb/gal flows in the tank at a rate of 4 gal/min. The mixture is kept well stirred and flows out of the tank at rate of 2 gal/min.
Compute the initial-value problem that desscribes the amount of salt in the tank.