Let's solve the expression:

$(3x^2 - 3x + 9) + (-5x^2 - 8x - 7)$

1. Combine the like terms:

• $3x^2$ and $-5x^2$
• $-3x$ and $-8x$
• $9$ and $-7$

2. Perform the addition:

$(3x^2 - 5x^2) + (-3x - 8x) + (9 - 7)$

$= -2x^2 - 11x + 2$

Thus, the simplified expression is:

$-2x^2 - 11x + 2$

Would you like more details on any step?

Here are 5 related questions you might find interesting:

1. How do you add polynomials with different degrees?
2. What is the significance of combining like terms?
3. How do you factor a quadratic expression like $-2x^2 - 11x + 2$?
4. How do you solve quadratic equations?
5. How do you perform polynomial long division?

Tip: Always align like terms vertically when adding or subtracting polynomials to avoid mistakes.