Answer:
The interval over which this formula give the average rate of change for f(x) is:
[3,7]
Explanation:
We know that when we are asked to find the average rate of change of the function f(x) over the interval [a,b] then the formula for the average rate of change is given by:

Here we have:
a=3 and b=7
Hence, the average rate of change is:

i.e.

Hence, the interval is: [3,7]