To find the mean of a group of data, you add up all of the numbers and divide the total by the amount of numbers there are. In this case, you have 15,11,10,11,14,10,15,10,and 12.
If you do cost per quantity you would get $9 over 6 visits. Then you divide both sides by 6 because to get to one by 6 it's 6 so when you divide both sides by 6 you would get 1.5 over 1 and all you do is add a zero because you're dealing with money
