Find the Exact Value of the Expression Using the Provided $\cos ( s + t )$

Find the exact value of the expression using the provided information.
-Find $\cos ( s + t )$ given that $\cos s = - \frac { 1 } { 6 }$ , with s in quadrant III, and $\cos t = - \frac { 3 } { 5 }$ , with $t$ in quadrant III.

A) $\frac { - 3 - 4 \sqrt { 35 } } { 30 }$
B) $\frac { 3 + 4 \sqrt { 35 } } { 30 }$
C) $\frac { 3 - 4 \sqrt { 35 } } { 30 }$
D) $\frac { 3 - 4 \sqrt { 37 } } { 30 }$

Correct Answer:

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