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.
[146.278, -96.446, -74.238, 86.029, -86.639, -67.42, 8.709]