Find All Fixed Points for the Function by Setting the Function

Multiple Choice

Find all fixed points for the function by setting the function equal to x and solving the resulting equation for x.
-A rug is to fit in a room so that a border of even width is left on all four sides. If the room is 15 feet by 17 feet and the area of the rug is 80 square feet, how wide will the border be?

A) 3.5 feet
B) 6 feet
C) 4.5 feet
D) 5.5 feet