The answer is D. 
Explanation:
I decided to start with 6 because it seemed to be the easiest. So you would out 6 in the place of ‘z’
6 ( 6 - 6 ) = 0 
Here you would do the parentheses first 
6 ( 0 ) = 0 
6 * 0 = 0
0 = 0
You’re not done bc it could be both 6 and -6 So input where ‘z’ is and you should get 
-6 ( -6 - 6 ) = 0
-6 ( -12 ) = 0
72 doesn’t equal 0 
Hope this helped