Adam D. answered 10/01/20
Patient and Knowledgeable Mathematics Instructor and Tutor
Chain rule tells us that if f(x)=g(h(x)), then f'(x) = g'(h(x)) h'(x).
So f'(8)=g'(h(8)) h'(8) = -9 g'(5), but we do not know g'(5), so there is not enough information, so you would enter impossible.