Question

Assume that f is a one-to-one function.

Answer 1

It is given in the question that f is a one-to-one function.

And for a one-to - one function,

If

$f(a)=b, \ then \ f^{-1} (b) =a$

So we will get

$a. If \ f(3)=15, \ then \ f^{-1} (15) =3 \\ b. If \ f^{-1}(6)=4, \ then \ f(4)=6$