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: [126.911, 177.371, 165.648, 112.523, 145.728, 229.829, -90.097]

123.988