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: [-81.316, -66.29, 129.505, 64.587, 54.295, 97.979, -90.49, -48.845, 221.481, 25.455]

30.636