Perimeter of rectangle: [tex]P=2a+2b[/tex]
Put in data given [tex]a=69[/tex] (height) and [tex]P=240[/tex] (perimeter)
[tex]240=2\times69+2b[/tex]
Now solve for b (width).
[tex]2b=240-2\times69[/tex]
[tex]b=\frac{240-2\times69}{2}=\boxed{51}[/tex]
It's width is 51 feet. Hope this helps.
r3t40