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.
[85.236, 109.509, -50.954, 191.838, -74.337, -3.426, 65.484]