Definition: 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.
Input: [244.1, -84.018, 7.772, 69.273, 99.397, 158.691, -0.315]

70.7