Write the Answer as a Single Term and Simplify $$\frac { 1 } { 3 } \left( \frac { 3 x } { x + 7 } \right) ^ { - 1 / 2 } \left( \frac { ( x + 7 ) ( 3 ) - 3 x } { ( x + 7 ) ^ { 2 } } \right)$$

Multiple Choice

Write the answer as a single term and simplify.
- $$\frac { 1 } { 3 } \left( \frac { 3 x } { x + 7 } \right) ^ { - 1 / 2 } \left( \frac { ( x + 7 ) ( 3 ) - 3 x } { ( x + 7 ) ^ { 2 } } \right)$$

A) $\frac { 21 } { ( 3 x ) ^ { 1 / 2 } ( x + 7 ) ^ { 3 / 2 } }$
B) $\frac { 7 } { ( 3 x ) ^ { 1 / 2 ( x + 7 ) ^ { 3 / 2 } } }$
C) $\frac { 3 x ^ { 1 / 2 } } { ( x + 7 ) ^ { 3 / 2 } }$
D) $\frac { 7 } { ( 3 x ) ^ { 1 / 2 } ( x + 7 ) ^ { 5 / 2 } }$