1. f(x+h)= (x+h)^2+ 13, not (x+h)^2= (x+h)(x+h)

2. -f(x)= -(x^2+ 13)= -x^2- 13, not -x^2+ 13

x^2 +2hx+h^2-x^2 +13/h

the two x^2 are cancelled

the h's cancel, leaving 2x+h+13/2

my final anwer was 2x+h+13/h

I didn't get it correct and im not sure where I went wrong...

Thanks!