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: [150.321, 169.658, 221.448, 54.785, 160.245, 9.534, 78.865, 229.753, 225.969]

144.509