Step 1: Concept
To find the inverse, set $y = f(x)$ and solve for $x$ in terms of $y$.
Step 2: Analysis
$y = 3x - 4 \Rightarrow y + 4 = 3x \Rightarrow x = \frac{y+4}{3}$.
Step 3: Conclusion
Replacing $y$ with $x$, we get $f^{-1}(x) = \frac{x+4}{3}$.
Final Answer: (A)