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: [139.6, 119.652, 135.338, 171.029, 247.554, 222.19, -61.931, 120.928, 235.688]

147.783