Answer
General equation is: $a_n=30+(-10)(n-1)$ and
$a_{20}=-160$
Work Step by Step
Formula to calculate the nth term of an arithmetic sequence is: $a_n=a_1+d(n-1)$
Here, $a_1: $ First term and $d=$ common difference
Since, we have $a_1=30$
Then, our General equation is: $a_n=30+(-10)(n-1)$
$a_{20}=30+(-10)(20-1)=30-190=-160$
