Hello!
To find the mean, you add up all of the numbers in a data set and then divide by the number of numbers in the set.
First of all, let's write down the data set from the picture.
5,6,6,6,6,7,7,8,8,8,8,9,9,9,9
Now we add them up and divide by the number of SUV's in the dealership (15).
111/15=7.4
Therefore, our mean is 7.4.
I hope this helps!