Answer
$f^{-1}(x) = 3x - 3$
Work Step by Step
$f(x) = \frac{1}{3}x + 1$
Let $f(x) = y$
$y = \frac{1}{3}x + 1$
$x = \frac{1}{3}y + 1$
$x = \frac{y}{3} + 1$
$3x = y + 3$
$3x - 3 = y$
$y = 3x - 3$
$f^{-1}(x) = 3x - 3$
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