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: [136.816, 121.886, 38.032, 81.322, -0.781, 112.95, 49.478, 219.21, -42.397]

79.613