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: [84.38, 108.119, 207.756, -40.156, -86.21, 20.753, 30.957, 90.529, -39.151]

41.886