Answer
$\mathrm{a}$.
Independent variable: $r$, dependent variable: $N$
$\mathrm{b}$.
$N(3)=13.49$
In 2012, there are 13.49 million housing units with 3 rooms.
Work Step by Step
$\mathrm{a}$.
$ N$ changes when $r$ changes, $r$ is arbitrary.
Independent variable: $r$, dependent variable: $N$
$\mathrm{b}$.
r=3 means that housing units with 3 rooms are observed.
Substitute r=3 into the expression for N:
$N(3)=-1.35(3)^{2}+15.45(3)-20.71$
$=-12.15+46.35-20.71$
$=13.49$ (million)
In 2012, there are 13.49 million housing units with 3 rooms.
