Given the function f (x) = 3^x, find the value of f^-1 (27)

This is asking you to solve the equation ...

... 27 = 3^x

You can use logarithms to find

... log (27) = x·log (3)

... log (27) / log (3) = x = 1.43136376 ... / 0.47712125 ...

... x = 3

Or, you can use your knowledge of small cubes and match exponents.

... 3^3 = 3^x

... 3 = x