A chemist has 20 gallons of solution with 12% saline. How much pure saline (100% saline) needs to be added to the 20 gallons to create a mixture with 15% saline content? Round your answer to the nearest tenth (if you answer this please let me know how you got the answer, thank you!)

Jack has a rectangular piece of land, the area of which is represented by a1 = 9.5l. his brother has a different rectangular piece of land, the area of which is represented by a2 = l(14 − l). let a represent the area in square meters and l represent the length in meters of the pieces of land. the two equations plotted on a graph meet at a point as shown in the image