Factor this by grouping. Group the first two terms together and then the second 2 terms together. The idea here is that, after grouping, what you can pull out in both groups is the same. Like this:
[tex]( x^{2} -9x)+(xy-9y)[/tex]
Now work on finding a common thing between the 2 groups:
[tex]x(x-9)+y(x-9)[/tex]
See, what you have in common there now is the (x-9) that you can factor out:
[tex](x-9)(x+y)[/tex]
And that is factored completely.
