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: [-20.161, -82.699, -55.493, 129.829, 14.679, 221.727, -18.924, 9.331]

24.786