The area of the rug is 9 by 7. Let's call the width of the border x. Therefore, the length of the rug will switch to 9 + 2x. The border is on both sides of it, so we add on 2x. Then, the width is 7 + 2x.
The area of the room is therefore: (9 + 2x)(7+ 2x).
We know the area of the room, so we can write and solve the following equation.