A rectangle's area is just the product of its base times its height. (A = bh) In this case, the area of her room's floor is 12 × 15 = 180 ft².
5/9 of 180 ft² is 100 ft².
A square IS a rectangle, so we can find the area with A=bh...but since all of the sides are the same length, we would just use A=s². Let's use what we know to solve for s.
A = s²
100 = s²
√100 = s
10 = s
