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.
[86.637, 50.043, 235.876, 53.937, 4.286, 149.072, 18.108, 76.563, -64.452]