Answer:
Assuming that you are asking for whether your answer is write or not, the answer is no. I am not sure what the x is for, but if you are asking for the mean of 8, 12, 15, and 11, the mean would not be 12.2 but 11.5.
To find that answer, you take all 4 of those numbers and add them together. After that, you take the total amount and divide them by how many numbers there are. In this case, it would be 4. 8+12+15+11=46. 46 divided by 4 = 11.5 which is the mean.