Using the perimeter of a rectangle, it is found that she can make a deck of 122 ft wide.
The perimeter of a rectangle of length l and width w is given by:
[tex]P = 2(l + w)[/tex]
In this problem:
Then:
[tex]P = 2(l + w)[/tex]
[tex]280 = 2(10 + 8 + w)[/tex]
[tex]36 + 2w = 280[/tex]
[tex]2w = 244[/tex]
[tex]w = \frac{144}{2}[/tex]
[tex]w = 122[/tex]
She can make a deck of 122 ft wide.
You can learn more about the perimeter of a rectangle at https://brainly.com/question/10489198