Answer:
the mean is 13
Step-by-step explanation:
The way to find the mean of a set of numbers is to add all the numbers together and divide the sum by the number of numbers. so 11 + 11 + 12 + 13+ 13 + 13 + 14 + 14 + 15 + 15 + 16 + 16 + 18 / 13 = 13.9
