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: [221.909, 38.36, -62.81, 132.751, -26.003, -12.857, 158.23, 243.071, 86.875, 71.632]

85.116