1. **State the problem:** Simplify the expression $8n + 12 + (-9) - (-6n)$. 2. **Recall the rules:** When subtracting a negative, it becomes addition: $-(-6n) = +6n$. Also, combine like terms (terms with $n$ and constant terms separately). 3. **Rewrite the expression:** $8n + 12 - 9 + 6n$. 4. **Combine like terms:** For $n$ terms: $8n + 6n = 14n$. For constants: $12 - 9 = 3$. 5. **Final simplified expression:** $14n + 3$.