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: [-15.115, 242.4, 228.135, 15.24, 92.757, -45.311, -70.8]

63.901