A 150 gallon tank initially contains 70 gallons of pure water. Water with a concentration of c pounds of salt per gallon is added to the tank at 2 gal/min, and theresulting solution leaves at a rate of 1 gal/min. Find the quantity, Q(t), of pounds of salt in the tank for times 0 t 80. What concentration c should be used so that the tank will have a concentration of 13 pounds per gallon once it is full with 150 gallons of water in the tank ?