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: [-64.17, 66.619, 131.319, 170.241, 186.539, 47.378, -56.022, 28.098, 20.752]

58.973