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: [-26.42, 131.449, 160.81, 216.055, 73.889, -21.603, -22.399, 105.801, 183.704]

89.032