The length of a rectangle is twice the width. The perimeter of the rectangle is 72 inches. To find the dimensions, you can let $\displaystyle{w}=\usepackage{cmbright}\Huge\$ the width, and then you will get two equations:

$\displaystyle{l}={2}{w}\usepackage{cmbright}\Huge\$

$\displaystyle{2}{l}+{2}{w}={72}\usepackage{cmbright}\Huge\$

Solve this system to find the dimensions of the rectangle.