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: [201.816, -9.972, 159.423, 203.688, 36.145, 78.098, 137.257]

115.208