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

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

A) $- \frac { 171 } { 221 }$
B) $- \frac { 21 } { 221 }$
C) $\frac { 21 } { 221 }$
D) $\frac { 171 } { 221 }$