The width of a rectangular garden is 9 feet, and its length is 12 feet. Three of these expressions equal the perimeter of the garden, in feet.
perimeter is calculated as follows
perimeter = sum of all the sides of the rectangle
rectangle consists of 4 sides of which longer sides are called the length - L and shorter side is the width - W. There are 2 lengths and they are equal and 2 widths and they are equal in size. perimeter = L + L + W + W = 2L + 2W
substituting the values in the equation P = 2L + 2W