Make a function statistic(list_of int) that takes as input a list of (exactly) three integers and returns a list of the following statistics: sum, average value, smallest value, largest value (in that order). For example:
>>> statistics([2, 8, 7])
[17, 5.666666666666667, 2, 8]
>>> statistics([11, 2, 11])
[24, 8.0, 2, 11]