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: [146.815, 125.411, 84.472, -63.01, 79.256, -34.213, 248.004, -86.96, -39.397]

51.153