Answer
$g^{-1}(x) = \log (\frac{x}{3.4})$
Work Step by Step
$g(x) = 3.4(10)^{x}$
Let $g(x) = y$
$y = 3.4(10)^{x}$
Swap the variables $x$ and $y$ and then solve for $y$ to find the inverse:
$x = 3.4(10)^{y}$
$\frac{x}{3.4} = (10)^{y}$
$y = \log_{10} (\frac{x}{3.4})$
$y = \log (\frac{x}{3.4})$
$g^{-1}(x) = \log (\frac{x}{3.4}).$