Answer
$a_n=-7+(n-1)4$
$a_{20}=68$
Work Step by Step
Recall:
The $n^{th}$ term ($a_n$) of an arithmetic sequence is given by the formula:
$$a_n=a_1+(nā1)d$$
where
$d$=common difference
$a_1$=first term
The given sequence has $a_1=-7$.
The common difference is $5-1=4$.
Thus, the general term of the given sequence can be found using the formula:
$$a_n=-7+(n-1)4$$
The $20^{th}$ term of the sequence can be found by substituting $20$ to $n$:
\begin{align*}
a_{20}&=-7+(20-1)4\\
&=-7+19(4)\\
&=-7+76\\
&=68
\end{align*}
