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: [69.721, 116.583, 63.325, -2.991, -54.502, -56.366, 169.392, 172.724, 185.307]

73.688