Find the Exact Value of the Expression Using the Provided $\tan ( \mathrm { s } - \mathrm { t } )$

Find the exact value of the expression using the provided information.
-Find $\tan ( \mathrm { s } - \mathrm { t } )$ given that $\cos \mathrm { s } = - \frac { 5 } { 13 }$ , with $\mathrm { s }$ in quadrant $\mathrm { II }$ , and $\sin \mathrm { t } = \frac { 8 } { 17 }$ , with $\mathrm { t }$ in quadrant II.

A) $\frac { 20 } { 3 }$

B) $- \frac { 140 } { 171 }$

C) $- \frac { 220 } { 171 }$

D) $- \frac { 20 } { 3 }$