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.
[18.08, 166.963, 187.434, 50.807, -19.266, 113.775, 4.423, 74.057, 166.081]