Rational expressions very simble, but hard for me

[physicsed]

$$\frac{5x-5y-bx+by}{5x-5y+bx-by}$$


i can't cancel anything

i can't factor anything

please help

 

[rock.freak667]

5x-5y=5(x-y)
do the same with b

 

[physicsed]

but the b's (x and y) doesn't cancel since they have two different signs

 

[Dick]

-bx+by=(-b)(x-y). (x-y) IS a factor of both the numerator and the denominator.