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: [86.723, 64.487, -59.274, 239.54, -44.729, 53.632, 209.626, -83.67, 103.072]

63.267