Answer: C. 27.3
Explanation:
The average rate of function f(x) from x = a to x = b is given by :-

The given function :

Now, the average rate of function f(x) from x = 3 to x = 15 is given by :-

Hence, the average rate of change from x = 3 to x = 15 for the given function = 27.3 .