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.
[74.43, 138.738, 114.237, 138.845, 188.957, 103.103, -43.988, -68.085, 157.274]