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: [128.899, -15.862, 152.639, 183.098, 75.752, 54.786, 159.782, 116.084, -36.669]

90.945