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.
[218.105, -89.34, 143.734, 105.746, -80.485, 139.21, -23.243, 85.283]