To determine the average rate of change of a given function over a given interval, we need to evaluate it in each of the extremes. In the given case, x = -3 and x = 6
Evaluating it, we have the following:

Now, to calculate the average rate of change, by using the following formula:

substituting x2 = 6 and x1 = -3, we have the following:

From the solution developed above, we are able to conclude that the average rate of the given function over the interval -3 ≤ x ≤ 6 is equal to:
4