If you divide a mural into 6 sections, and paint each section with 3 gallons of paint per section, that means you are using 3 gallons of paint 6 times.
3 x 6 = `18
Therefore, you will be using 18 gallons of paint for the mural, and when you subtract 18 gallons from the original 32 gallons of paint, you get 14 gallons left over.