Answer:
B
Step-by-step explanation:
The average rate of change of f(x) in the closed interval [ a, b ] is
[tex]\frac{f(b)-f(a)}{b-a}[/tex]
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 = [tex]\frac{27-3}{3-1}[/tex] = [tex]\frac{24}{2}[/tex] = 12 → B
