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: [144.721, 240.842, -61.62, 128.1, 66.188, 74.919, 214.142, 186.413, 215.112]

134.313