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: [-31.252, 246.934, 96.512, 19.356, -50.759, 134.528, 176.914, 17.007, 171.802]

86.782