Step 1: Concept
Observe if the numerator is the derivative of the denominator.
Step 2: Analysis
Let $f(x) = 9e^x - 4e^{-x}$.
$f'(x) = 9e^x - 4(e^{-x} \cdot -1) = 9e^x + 4e^{-x}$.
Step 3: Conclusion
The integral is of the form $\int \frac{f'(x)}{f(x)} dx = \log|f(x)| + C$.
Result $= \log|9e^x - 4e^{-x}| + C$.
Final Answer: (E)