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: [171.439, 0.981, 42.253, 239.995, 129.938, -67.125, -69.565, -53.374, -51.357]

38.132