Answer:
Elissa needs 4 quarts of paint, or 1 gallon.
Explanation:
Elissa's room is in the shape of a rectangular prism. Assuming that she will only be painting the walls and not the floor or ceiling, you just need to calculate the area of the four walls - front and back and side to side. Based on the dimensions given, the area of Elissa's front and back walls are 8 ft x 9 ft or 72 ft² for each wall. Since there are two, we take that area times two: 72 x 2 = 144 ft².
Elissa's side walls are 8 ft x 13 ft or 104 ft² for each wall. Since there are two, we take this area times two: 104 x 2 = 208 ft².
To find the total area needed to paint, we add all four walls: 144 + 208 = 352 ft². Since a quart of paint covers 100 ft² and a gallon covers 400 ft², Elissa can either purchase 4 quarts of paint or 1 gallon to paint her bedroom.