Answer
$f^{-1}(x) = \log_4 x$
Work Step by Step
$f(x) =4^{x}$
Let $f(x) = y$
$y = 4^{x}$
Swap the $x$ and $y$ variable to find the inverse:
$x =4^{y}$
$y = \log_4 x$
$f^{-1}(x) = \log_4 x$
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