Final answer:
To calculate the amount of decorative molding needed for the room, find the perimeter of the rectangular room by adding together the lengths of all four sides. The perimeter for a room that is 12 ft by 8 ft is 40 ft, which is the total length of molding required.
Step-by-step explanation:
To find the length of decorative molding needed to edge the top of the walls in a rectangular room, you must calculate the perimeter of the room. The room in question is 12 ft long and 8 ft wide. To determine the perimeter, you add together the lengths of all four sides: Perimeter = 2×(length + width).
The calculation is therefore: Perimeter = 2×(12 ft + 8 ft) = 2×(20 ft) = 40 ft. Thus, the correct amount of decorative molding needed is 40 feet, which corresponds to choice (c).