#### Answer

a. Average ticket price: ${{\$}} 4.22$, which is an understimate of the value in the graph by ${{\$}} 0.01.$
b. Average ticket price: ${{\$}} 7.22$, which is an understimate of the value in the graph by ${{\$}} 0.63$

#### Work Step by Step

$a.$
In 1990, (10 years after 1980), $ n=10.$
Substituting into the formula,
$T=0.15(10)+2.72$
$=1.5+2.72$
$=1.50 +2.72$
$=4.22$
The graph reads a value of $4.23$, so the model underestimates the graph by $0.01$
$(4.23-4.22=0.01)$
$b.$
In $2010$, ($30$ years after 1980), $ n=30.$
Substituting into the formula,
$T=0.15(30)+2.72$
$=4.50+2.72$
$=7.22$
The graph reads a value of $7.85$, so the model underestimates the graph by $0.63$
$(7.85-7.22=0.63)$