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.
[-17.064, 1.578, 120.654, -50.179, 111.345, 76.062, 132.241, 22.805, 30.414]