A tank haves 100 gallons of pure water. Brine having 2 lb of salt per gallon is added to the tank at the rate of 5 gal/min.
a) How much salt is present after 20 min if the well stirred mixture runs out at 6 gal/min?
b) Determine the maximum number of pounds of salt the tank will contain and the number of minutes needed to reach the maximum value.