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: [-54.897, 241.797, 213.609, 49.526, 248.389, 136.498, 18.475, 246.026]

137.428