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: [103.22, 185.904, -17.334, 225.815, -36.87, 49.503, 122.265, -67.533, 13.831]

64.311