Inverse function problem?

The derivative dx/dy of f^(-1) is 1/(dy/dx) at the corresponding point.

It's telling you this is where x = 1 and y = 9 on the original function f(x). So do these steps:

Take the derivative of y = x^3 + 3x^2 + 5 at x = 1.
Take its reciprocal.

The answer is as follows :

f(1) = 9, so assuming f inverse exists, f^-1(9) = 1.