Answer:
Mr. Ross will need 3 3/4 gallons of paint to paint the entire wall.
Explanation:
First, multiply 142.5 by 1/5, which equals 28.5. Now you know how many square feet he painted with 3/4 of the gallon. Divide 28.5 by 3/4, or multiply 28.5 by 4/3. This equals 38, so each gallon will paint 38 square feet. Divide 142.5 by 38, and you will get 3.75. Not sure if you need to change it to a fraction or not, but if you do, it's 3 3/4.