Explanation:
i just answered this.
the average change rate is the change of the functional result in a given interval relative (= divided by) to the length of the interval of the input variable.
in short
( f (interval upper limit) - f (interval lower limit) ) /
(interval upper limit) - (interval lower limit)
upper limit = 0
lower limit = -2
the functional values (y) are 6 and 10 at these points.
so, we get
(6 - 10) / (0 - -2) = -4 / 2 = -2