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.

[-9.355, 74.387, 197.588, 158.546, 169.913, 142.404, 9.344, 104.466, 23.51, -12.47]
85.833