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: [28.183, 142.599, 154.348, 0.839, 53.995, -28.433, -90.398]

37.305