Answer:
The total area of the back classroom wall is (20ft x 12ft) = 240ft²
The paint coverage is usually rated by area coverage. For example, one gallon of paint is expected to cover 400 ft².
Assuming a gallon of paint will cover 400ft², she will need (240ft²/400ft²) = 0.6 gallon of paint to cover the entire wall.
Mrs. Jones will need 0.6 gallon of paint to paint the back classroom wall.
