## Geometry: Common Core (15th Edition)

$9$
We rewrite the given ratio as a fraction: $\frac{9x-9y}{x-y}$ Next, we find a common factor that is in both the numerator and the denominator, and factor it out: $\frac{9(x-y)}{1(x-y)}$ When you divide any number by itself, you get $1$. Therefore, we can cancel out the common factor. This leaves us with $\frac{9}{1}=9$.