For this problem, f(x) = -x2+2x-1
To start, this is
f(x+h)-f(x)h=-(x+h)2+2(x+h)-1 - (-x2+2x-1)/h
In the numerator, you should expand the binomial, distribute, when subtracting you should distribute the minus. When done, anything without an "h" in the numerator should be gone. If not, there is an error.
Then, factor out an "h" from the numerator and cancel it with the denominator.