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: [-51.782, 108.911, -66.107, 149.563, 19.229, -83.242, 134.687, 226.31, 133.983]

63.506