To evaluate the function $f(x) = 3x - 2x$ at $x = -3$:

1. Start by substituting $x = -3$ into the equation: $f(-3) = 3(-3) - 2(-3)$

2. Now simplify each term: $3(-3) = -9 \quad \text{and} \quad 2(-3) = -6$

3. Subtract the terms: $-9 - (-6) = -9 + 6 = -3$

Thus, the value of $f(x)$ when $x = -3$ is $-3$.

Let me know if you'd like further details!

Here are some related questions:

1. What happens if you switch the signs in the function?
2. Can you evaluate $f(x) = 4x - 5x$ at $x = 2$?
3. What is the result of $f(x) = 3x + 2x$ when $x = 5$?
4. How does adding a constant affect the function?
5. What if $f(x) = 3x^2 - 2x$, how does it change?

Tip: Always simplify the equation as much as possible before substituting values!