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: [21.445, -36.626, 184.86, 72.243, 229.642, -85.168, 133.183, 9.889, 222.113]

83.509