Answer:
-11.4
Explanation:
To find the mean:
1. Add all the numbers up: -12+-12+-9+-11+-13 = -57
2. Divide the added numbers by the amount of numbers you added together (which would be 5): -57/5 = -11.4
3. After dividing you have your answer. Next step would be to round, that is not needed for this problem.
Hope this helps!