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: [-85.469, -13.4, 204.437, 105.267, -65.813, 21.201, -13.486]

21.82