Answer:
11
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, b ] = [ 3, 5 ]
f(b) = f(5) = 5² + 3(5) - 12 = 25 + 15 - 12 = 28
f(a) = f(3) = 3² + 3(3) - 12 = 9 + 9 - 12 = 6
Hence
average rate of change = [tex]\frac{28-6}{5-3}[/tex] = [tex]\frac{22}{2}[/tex] = 11
