A campground consists of 9 square campsites arranged in a line along a beach. The distance from the edge of a campsite to the water at the end of the beach is 5 yd. The area of the campground, including the beach, is 1115 sq yd. What is the width of one campsite?

We know that each campsite is a square; we also know that all the sides of a square are equal; therefore the length and the width of each campsites are equal. Lets label [tex]x[/tex] to each side of our campsite. From the problem we know that the distance from the edge of a campsite to the water at the end of the beach is 5 yd, so the distance including our campsite will be [tex]5+x[/tex]. Also, since each campsite have length=x, the total length of the 9 campsites will be [tex]9x[/tex]. Now we have a big rectangle including the campground and the beach of length=[tex]9x[/tex] and width=[tex]5+x[/tex].  The area of a rectangle is [tex]A=(length)(width)[/tex], and from our problem we know that area is 1115 square yards, so we can set up an equation and solve for [tex]x[/tex] to find the width of each campsite:
[tex]1115=(9x)(5+x)[/tex]
[tex]1115=45x+9 x^{2} [/tex]
[tex]9 x^{2} +45x-1115=0[/tex]
Using the quadratic formula to solve the equation, we get that:
[tex]x=8.9[/tex] or [tex]x=-13.9[/tex]
Since distances cannot be negative, the solution is [tex]x=8.9[/tex]

We can conclude that the width of each campsite is 8.9 yards.