Just group everything and "cancel" things out. So you would have
[(x+5)(9x^2)] / [(3x)(x+5)]
so here you can so the (x+5) on the top and the bottom divide out and become 1.
so now you'd be left with
(9x^2) / (3x)
here you can divide one of the x's out( x^2/x=x) so that one is left on the top and 9/3=3.
so your answer in the end should be 3x.
Hope this helps:)