Rational Expressions with unlike denominators

[Desan65]

The dimensions of a rectangle are 5/(3-y) and 7/(y(squared) - 9). Find the perimeter of the rectangle. I factored the y(squared) - 9 to (y-3) and (y+3), but then I got stuck because 3-y is not the same as y-3, so I couldn't eliminate it. Where do I go from here?

 

[pappus]

The dimensions of a rectangle are 5/(3-y) and 7/(y(squared) - 9). Find the perimeter of the rectangle. I factored the y(squared) - 9 to (y-3) and (y+3), but then I got stuck because 3-y is not the same as y-3, so I couldn't eliminate it. Where do I go from here?

\(\displaystyle \displaystyle{3-y = (-1) \cdot (y-3)}\)