The length of the rectangle is 6 cm what is the area if the perimeter is 18 cm.

1. Find the width of the rectangle by the formula a = (P – 2b) / 2, where P is the perimeter of the rectangle, and and b are its adjacent sides:
a = (18 – 6 * 2) / 2 = (18 – 12) / 2 = 6/2 = 3 cm.
2. Find the area of a rectangle by the formula S = ab, where S is the area of a rectangle with sides a and b:
S = 6 * 3 = 18 cm2.
Answer: the area of the rectangle is 18 cm2.