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: [149.739, -36.895, 224.494, 183.888, 76.457, 207.401, -53.838, 249.378, 161.735, 216.549]

137.891