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.
[-3.56, 159.692, 192.288, 188.355, 42.29, -70.831, 174.258, 28.121]