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: [158.787, 159.947, 57.37, 138.776, 215.233, 82.571, -69.464]

106.174