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: [19.988, 41.712, -73.64, 121.088, 210.071, 220.448, 131.894, 53.952, 89.133]

90.516