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.
[121.694, -90.704, -1.617, 187.202, 26.062, 106.371, 235.249, 42.346, -89.297]