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: [216.998, 178.72, -56.339, 16.194, -25.704, -74.26, 58.073, 35.27, 148.949]

55.322