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: [183.31, 129.131, 84.609, -82.146, 216.028, -95.014, 105.812, 137.712, -78.8]

66.738