Area of a deck is 680 square feet. The deck's width is 17 feet. What is its perimeter

First you need to find the length

L=680/17=40

Then you would add all 4 sides together (I'm assuming that the deck is a rectangle as you gave the width and area and the area formula using width is A=LW)

17+17+40+40=114

The deck's perimeter is 114ft