Answer
$a_{n}=3n-12$
$a_{30}=78$
Work Step by Step
The first term is $-9$ and the common difference is $-6-(-9)=3$.
Equation for an arithmetic sequence is
$a_{n}=a_{1}+(n-1)d $
where $a_{1}$ is the first term and $d$ is the common difference.
$a_{n}=-9+(n-1)(3)$
$a_{n}=-9+3n-3=3n-12$
$a_{30}=3(30)-12=78$
