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: [18.604, -86.842, -18.702, 15.142, -22.132, 153.856, 173.481, 192.066, -65.509]

39.996