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: [77.489, -7.259, 13.133, 54.234, -79.321, -70.512, -28.704, -90.5]

-16.43