The perimeter of the rectangle is 28 dm, and its length is 9 dm. Find the area of the rectangle.

The perimeter of a rectangle is equal to the sum of all its sides P = a + b + c + d. Since the opposite sides of the rectangle are equal, then P = 2 * a + 2 * b. Substituting the known values of the perimeter and one of the sides, we can find the length of the second side: 28 dm = 2 * 9 dm + 2 * h, 28 dm = 18 dm + 2 * h, 2 * h = 28 dm – 18 dm, 2 * w = 10 dm, w = 10 dm: 2, w = 5 dm. The area of the rectangle is equal to the product of length and width: S = a * b, S = 5 dm * 9 dm = 45 sq dm.
Answer: the area of the rectangle is 45 sq. Dm.