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: [153.539, -51.583, 173.264, 213.663, 211.19, 216.358, 237.361, -57.464]

137.041