The following list gives the number of public libraries in each of 12 counties \[ 11,11,7,7,8,7,8,9,8,9,10,9 \] Find the modes of this data set. If ther is more than one mode, Write them seperated by comas. I there is no mode, click on "No mod"

Step 1 ：The given data set is [11, 11, 7, 7, 8, 7, 8, 9, 8, 9, 10, 9].

Step 2 ：The mode of a data set is the number that appears most frequently.

Step 3 ：Count the frequency of each number in the list: {7: 3, 8: 3, 9: 3, 11: 2, 10: 1}.

Step 4 ：The numbers with the highest frequency are 7, 8, and 9, each appearing 3 times.

Step 5 ：Final Answer: The modes of this data set are \(\boxed{7, 8, 9}\).