Answer:
g(-6) = 8; g(0) = 5; g(6) = 0; g(12) = 6
Explanation:
We assume your function definition is ...

For each given value of x, determine which segment applies, then evaluate.
For x = -6 and for x = 0, the first segment applies:
g(-6) = (-1/2)(-6) +5 = 3 +5 = 8
g(0) = (-1/2)(0) +5 = 5
For x = 6 and x = 12, the second segment applies:
g(6) = (6) -6 = 0
g(12) = (12) -6 = 6
In summary, ...
g(-6) = 8; g(0) = 5; g(6) = 0; g(12) = 6