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.
[234.845, 147.416, -70.399, 85.937, -81.106, 42.946, 39.64]