Answer:
13
Step-by-step explanation:
The average rate of change of a function f(x) in the closed interval [ a, b ] is
[tex]\frac{f(b)-f(a)}{b-a}[/tex]
here [ a, b ] = [ 3, 9 ]
f(b) = f(9) = 9² + 9 - 6 = 84
f(a) = f(3) = 3² + 3 - 6 = 6
average rate of change = [tex]\frac{84-6}{9-3}[/tex] = [tex]\frac{78}{6}[/tex] = 13
