Answer:
The correct option is C.
Explanation:
The average rate of change of f(x) over the interval [a, b] is defined as

Substitute a=8 and b=12 in the above formula to find the average rate of change of f(x) over the interval [8, 12].

The average rate of change of f(x) over the interval [8, 12] is
.
Therefore the correct option is C.