Arectangular billboard is 30 feet by 18 feet. if a gallon of paint covers 250 square feet, how many gallons should be purchased to cover the entire board? a: 1 b: 2 c: 3 d: 4

The "square feet" that the paint covers refers to the area of the billboard.  If the billboard is 30 x 18, then its area is those 2 numbers multiplied together.  The area of the billboard is 540.  If one gallon of paint covers 250 square feet, then we need 540/250 gallons, which is 2.16.  If you have to buy the paint by the gallon, then you will need 3 because you are going to use .16 of a third gallon.