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: [-17.508, 162.093, 118.367, 84.373, 156.946, 157.234, 222.37, 72.338, 220.575]

130.754