Use a Sum or Difference Identity to Find the Exact $\cot \theta$

Multiple Choice

Use a sum or difference identity to find the exact value.
-Find $\cot \theta$ if $\tan \theta = \frac { \sqrt { 7 } } { 3 }$ and $\theta$ is in quadrant III.

A) $\frac { 3 \sqrt { 7 } } { 7 }$
B) $- \frac { 3 } { 2 }$
C) $\frac { 5 } { 4 }$
D) $- \frac { \sqrt { 7 } } { 9 }$