Answer:
B
Explanation:
The average rate of change of f(x) in the closed interval [ a, b ] is

Here a = 1 and b = 3
f(b) = f(3) = 27 ← value of y corresponding to x = 3
f(a) = f(1) = 3 ← value of y corresponding to x = 1, thus
average rate of change =
=
= 12 → B