The given expression is:

$-3a - (6b - 9c)$

Let's simplify it step by step.

1. Distribute the negative sign through the parentheses: $-3a - 6b + 9c$

There are no like terms to combine, so the simplified expression is:

$-3a - 6b + 9c$

Would you like any further explanation?

Here are 5 related questions to explore:

1. How do you combine like terms in algebraic expressions?
2. How does distributing a negative sign affect the terms inside parentheses?
3. Can you factor common terms out of the expression $-3a - 6b + 9c$?
4. What are some strategies for simplifying more complex algebraic expressions?
5. How do operations on variables differ from operations on numbers?

Tip: Always be mindful of the signs when distributing over parentheses, especially negative signs!