A 400-gal tank initially contains 100 gal of brine, containing 50 lb of salt. Brine containing 1 lb of salt per gallon enters the tank at a rate of of 5 gal/s, and the well mixed brine in the tank flows out at the rate of 3 gal/s. Both inflow and outflow stop when the tank is full. (a) Find the volume of the brine in the tank after t seconds. (b) Find the amount of salt in the tank after t seconds. (c) How much salt will the tank contain when it is full?