How to model 23 less than 55 on a number line

You are updating your garage and the only thing left to paint is your garage day. you're only going to paint the slide that faces the street. the garage door is 9 fert 8inches tall and 120 inches wide. you need to know the surface area of the side of the garage door to determine how much paint to buy. the hardware store sells paint by how much covers a square foot. what is the surface area you should report to the hardware store what is the answer