Answer
$f^{-1}(x)=\frac{1}{x}$
Work Step by Step
$f(x)=\frac{1}{x}$
$y=\frac{1}{x}$
a.
$x=\frac{1}{y}$
$y=\frac{1}{x}$
$f^{-1}(x)=\frac{1}{x}$
b.
$f(f^{-1}(x))=\frac{1}{\frac{1}{x}}=x$
and
$f^{-1}(f(x))=\frac{1}{\frac{1}{x}}=x$