It's 13.5 because you put them in order and then you have 13 and 14 you add them together and then divide by 2
So you first have to order them least to greatest, which would be : 8 , 9 , 13, 14 , 15, 16. Since the number of numbers is even, average the 2 middle numbers. This is 13 + 14 divided by 2 or 13.5.
