Answer:
z + 12
Explanation:
This is the answer because:
1) Our like terms are 2z and z and 9 and 3
2) First, we should add 9 and 3 because they are like terms and there is a + sign in front of the 3 which equals to 12
3) Then, subtract 2z and z because they are like terms and there is a - sign in front of the z which equals to z
4) Finally, we are left with z + 12. This expression is simplified because there is no more like terms
Hope this helps!