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: [29.28, 238.933, 229.916, 95.678, -5.517, 148.697, 249.423, -67.735, 21.392]

104.452