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: [84.541, -70.824, -9.953, 64.465, 208.875, 25.429, 81.195, 22.43, 87.39]

54.839