More rational expressions. I am trying to understand this but...

Find the LCD for the given and convert each into an equivalent rational expression with teh LCD as the denominator.

4 , 5x

---- --------

x-y 2y-2x

I factored what could be to get

4 , 5x

---- --------

x-y 2(y-x)

now I think the LCD is 2(y-x)

The next problem is

3 2b -5

---------- , --------- , -----------

4b^2 - 9 2b + 3 2b^2-3b

I factored what I could (I think)

3 2b -5

---------- , --------- , -----------

4b^2 - 9 2b + 3 b(2b-3)

Thanks again for your help!!