What do you mean by "any calculus like that"? If you are asked this question, surely you have worked with derivatives and the chain rule? If g is the inverse function to f, then f(g(x))= x so, by the chain rule, f'(g(x))g'(x)= 1. g(2)= 1 because has 1 as an obvious root. f'(g(2))= f'(1) which is . So 5g'(2)= 1, g'(2)= 1/5.