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.
[-26.162, -54.388, 210.418, 243.645, -47.413, 127.634, -7.886]