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: [-29.727, 150.587, -28.344, 181.096, 0.275, -91.658, 169.609, -21.106, 153.48]

53.801