## Thinking Mathematically (6th Edition)

perimeter = $30 \text{ cm}$
RECALL: (1) The perimeter of a polygon is equal to the sum of all the lengths of its sides. (2) Opposite sides of a rectangle have equal lengths. Using (2) above, the unknown side lengths are 9 cm and 6 cm. Thus, the perimeter of the rectangle is: $=(9+9+6+6) \text{ cm} \\=30 \text{ cm}$