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: [-3.914, 130.866, 20.311, 206.531, 173.235, -43.858, -78.715, 117.81, 73.103]

66.152