Find the Exact Value of the Expression Using the Provided $\sin \theta$

Multiple Choice

Find the exact value of the expression using the provided information.
-Find $\sin \theta$ if $\sec \theta = - \frac { 8 } { 5 }$ and $\tan \theta < 0$ .

A) $- \frac { \sqrt { 39 } } { 8 }$
B) $\frac { \sqrt { 39 } } { 8 }$
C) $- \frac { 5 } { 8 }$
D) $\frac { 39 } { 64 }$