#### Answer

The length is 18 feet and the width is 9 feet.

#### Work Step by Step

Since the width is stated in terms of the length, we can let l represent the length. Since the width is one-half its length, and the length is l, the the width is $\frac{1}{2}l$.
The formula for the perimeter of the rectangle is width + width + length + length
The perimeter of the rectangle is 54, so we set up the following equation:
l + l + $\frac{1}{2}$l + $\frac{1}{2}$l = 54
3l = 54
Divide both sides by 3.
l = 18
Since the length is 18, the width is $\frac{1}{2}$l = $\frac{1}{2}$ $\times$ 18 = 9.