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.

[21.325, 193.326, 140.579, 157.214, 129.438, 205.186, -8.892, 154.529, 241.713]
137.158