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: [189.969, 141.874, -63.201, -22.618, 183.145, -36.312, 55.276, 125.444, -89.031]

53.838