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.
[-64.822, 73.832, 12.429, 21.749, 184.434, 98.367, 241.998, 67.573, 115.104]