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: [249.224, 40.768, 197.558, 206.868, 119.722, -23.108, 122.159, 166.539, 14.859]

121.621