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: [217.166, 115.156, -10.911, 183.125, -16.943, 175.079, 108.195, -38.436, 26.241]

84.297