Answer
$a.\quad W=173n+293$
$b.\quad 1850$ million, which overstimates the actual value by 98 million.
Work Step by Step
a.
$ W=3(50n+95)+2(\displaystyle \frac{23}{2}n+4)\qquad$... distribute
$ W=(150n+285)+(23n+8)\qquad$... get rid of parentheses
$ W=150n+285 + 23n+8 \qquad$...rearrange and group like terms
$W=(150n+23n)+(285+8)$
$W=173n+293$
b.
In $2009$ (9 years after 2000), $n=9$. Substituting,
$W=173(9)+293$
$=1557+293$
$=1850$ (million)
The graph shows 1752 million for 2009,
so our model overestimates the actual number by
$1850-1752=98 $ (million)
