How many gallons of paint are needed to paint the walls of a rectangular prism-shaped room that is 20 ft by 10 ft and 8 ft high if 1 gallon of paint covers 40 sq ft.?

  12 gallons

Step-by-step explanation:

The perimeter of the room is ...

  20 ft + 10 ft + 20 ft + 10 ft = 60 ft

Then the area of the walls is the product of this and their height:

  area = (60 ft)(8 f) = 480 ft²

The number of gallons required is ...

  (480 ft²)/(40 ft²/gal) = 12 gal

12 gallons of paint are required.