Find a Formula For $a _ { n }$ For the Arithmetic Sequence

Multiple Choice

Find a formula for $a _ { n }$ for the arithmetic sequence.
$$a _ { 4 } = - 13 , a _ { 13 } = - 31$$

A) $a _ { n } = - 7 - 2 n$
B) $a _ { n } = 5 - 7 n$
C) $a _ { n } = - 2 - 7 n$
D) $a _ { n } = - 7 ( - 2 ) ^ { n }$
E) $a _ { n } = - 5 - 2 n$