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: [11.296, 158.438, 240.51, -84.899, 136.207, 133.716, -66.861]

75.487