A large tank is partially filled with 100 gallons of fluid in which 20 pounds of salt is dissolved. Brine containing

1
2
pound of salt per gallon is pumped into the tank at a rate of 6 gal/min. The well-mixed solution is then pumped out at a slower rate of 4 gal/min. Find the number of pounds of salt in the tank after 45 minutes. (Round your answer to two decimal places.)