By f(x)=x^-3(x^(-1)+1) do you mean ?

Whether you do or don't, the thing is that you've calculated f(1) when the question requires f'(1), that is, the value of the derivative of f(x) calculated at x = 1.

If my guess for your function is correct, then my simplification makes it clear that you should apply the quotient rule to get the derivative .....