Problem: A chemical company needs to paint twenty chemical tanks including the top and the bottom of the tanks. Each tank has a height of 11 ft and a diameter of 6 ft. Paint can be purchased in 1-gallon cans or in 5-gallon cans that cost the same as 4 1-gallon cans. Each gallon of paint will cover 350 square feet. How many of each should be purchased to keep the cost of painting the tanks as low as possible? Provide justifications and citations for your responses.