Answer
$f^{-1}(t) = \log_2 3t$
Work Step by Step
$f(t) = \frac{1}{3}(2)^{t}$
Let $f(t) = y$
$y = \frac{1}{3}(2)^{t}$
Swap the $t$ and $y$ variable to find the inverse:
$t = \frac{1}{3}(2)^{y}$
$t = \frac{2^{y}}{3}$
$3t = 2^{y}$
$y = \log_2 3t$
$f^{-1}(t) = \log_2 3t$