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: [228.646, -26.004, 175.415, 53.329, 5.579, 89.641, 19.887, 103.431, -78.426]

63.5