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.
[-51.39, 186.421, -58.942, 54.292, 212.592, 101.924, -57.492]