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: [207.117, 121.279, 23.27, 231.597, -49.636, 28.83, 84.584, -87.796, 19.494]

64.304