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: [-3.91, 22.742, 46.288, -49.853, 149.36, 175.956, 225.821, -17.566, -56.963]

54.653