Answer
$a_{n}=12-n$
$a_{30}=12-30=-18$
Work Step by Step
The first term is $11$ and the common difference is $-1$.
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.
$a_{n}=11+(n-1)(-1)$
$a_{n}=11+(1-n)=12-n$
$a_{30}=12-30=-18$
