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: [-7.209, -20.712, 59.85, 122.982, 157.661, -81.04, 174.833, 167.565, 156.9]

81.203