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.
[-30.799, -64.686, -69.902, 119.235, 53.564, -51.703, 225.429, -78.343]