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: [105.274, -66.492, 118.244, 114.355, -14.847, -3.061, 221.289, 42.404, -7.31]

56.651