1. **State the problem:** Factor the expression $6a - 9$ by extraction. 2. **Formula and rule:** To factor by extraction, find the greatest common factor (GCF) of all terms and factor it out. 3. **Find the GCF:** The terms are $6a$ and $9$. The GCF of $6$ and $9$ is $3$. 4. **Extract the GCF:** Write the expression as $3(\frac{6a}{3} - \frac{9}{3})$. 5. **Simplify inside the parentheses:** $3(2a - 3)$. 6. **Final answer:** The factored form of $6a - 9$ is $3(2a - 3)$. This method helps simplify expressions by taking out common factors.