Perform the Indicated Operation $$\left( \frac { x } { x + 3 } - \frac { x } { x - 3 } \right) \div \frac { x } { 7 x + 21 }$$

Multiple Choice

Perform the indicated operation. Simplify if possible.
- $$\left( \frac { x } { x + 3 } - \frac { x } { x - 3 } \right) \div \frac { x } { 7 x + 21 }$$

A) 0
B) $- \frac { 42 } { ( x - 3 ) }$
C) 14
D) $- \frac { 6 x ^ { 2 } } { 7 ( x + 3 ) ^ { 2 } ( x - 3 ) }$