Simplify if possible x^2+17x/x^2-9x+x^2-10x/x^2-9x

Assuming you mean

(x^2+17x)/(x^2-9x) + (x^2-10x)/(x^2-9x)
you can factor out the x's giving
(x+17)/(x-9) + (x-10)/(x-9)
= (x+17+x-10)/(x-9)
= (2x+7)/(x-9)