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: [91.456, 16.428, 217.399, 13.594, -22.488, 4.119, 88.493]

58.429