A tank has a capacity of 400 gallons and initially has 100 gallons of a solution that has 40 lb. of dissolved salt. A brine solution with a concentration of 2 lb. of salt per gallon is pumped into the tank at a rate of 5 gallons per minute and the well-stirred solution is drained at the same rate. a) Find the amount of salt in the tank when t = 15 minutes b) Find the amount of salt in the tank when the tank is full.