Find the Indicated Term of the Arithmetic Sequence Based on the Given

Multiple Choice

Find the indicated term of the arithmetic sequence based on the given information.
- $a _ { 1 } = 13$ and $a _ { 18 } = - 55 ;$ Find $a _ { 9 }$

A) $- 91$
B) $- 19$
C) $- 55$
D) $- 23$