Answer:
9a - 18
Explanation:
3a + 6a - 27 +9
→ gather like terms
(3a + 6a) + (-27 +9)
→ collect coefficients of like terms
(3 + 6) × a + (-27 +9)
→ calculate the sum/difference
9a + (-27 +9)
→ calculate the sum/difference (again)
9a - 18
Answer: 9a - 18
hope this helps!