Answer:
40
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 ] = [ 7, 8 ] , then
f(b) = f(8) = 20 ← point (8, 20 ) on graph
f(a) = f(7) = - 20 ← point (7, - 20 ) on graph
average rate of change = [tex]\frac{20-(-20)}{8-7}[/tex] = [tex]\frac{20+20}{1}[/tex] = 40
