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.
[209.45, 150.578, 223.793, 129.673, 104.211, 55.63, 103.41, -68.055]