First, think that there are 12 part of the wall, and that one part (1/12) needs 1/4 gallon of paint. Since there are 12 parts, you need to do 12 times 1/4 of 12/1 times 1/4 to 12/4. 12/4 = 3. So therefore, 3 gallons are needed to paint the entire wall.
