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: [147.895, -56.992, 16.321, -86.823, 2.268, 170.796, 217.458, 143.801, 221.719]

86.271