It seems like there is a typo in the function you've provided. I assume you meant to write $f(x) = 9x^2 - x^3$. I'll proceed with finding the derivative of this function.

The function is: $f(x) = 9x^2 - x^3$

To find the derivative $f'(x)$, we differentiate each term of the function with respect to $x$:

1. The derivative of $9x^2$ is $18x$.
2. The derivative of $-x^3$ is $-3x^2$.

So, the derivative of the function is: $f'(x) = 18x - 3x^2$

Would you like any details or have any questions?

Here are 5 related questions for further practice:

1. What is the derivative of $f(x) = 5x^3 + 2x^2 - x$?
2. Find the second derivative of $f(x) = 9x^2 - x^3$.
3. Calculate the derivative of $g(x) = x^4 - 4x^2 + 7$.
4. What is the slope of the tangent line to the curve $f(x) = 9x^2 - x^3$ at $x = 2$?
5. Find the critical points of $f(x) = 9x^2 - x^3$.

Tip: Always check your function for typos or errors before differentiating, as a small mistake can change the entire solution!