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: [-86.961, -47.951, 143.862, 44.642, 144.616, 187.7, 183.32]

81.318