Definition: In this task you will be given a list of numbers and you need to find the mean (average) of that list. The mean of a list can be found by summing every number in the list then dividing the result by the size of that list. The output should be rounded to 3 decimal places.
Input: [-16.468, -91.848, 81.92, -63.148, 64.163, -63.179, 155.614, -18.748, -99.73]

-5.714