Perform the Indicated Operation $\frac { 4 } { a + 6 } - \frac { 3 } { a }$

Multiple Choice

Perform the indicated operation. Simplify, if possible. $\frac { 4 } { a + 6 } - \frac { 3 } { a }$

A) $\frac { 1 } { a ( a + 6 ) }$
B) $\frac { 13 } { a ( a + 6 ) }$
C) $\frac { a + 6 } { a ( a + 6 ) }$
D) $\frac { a - 18 } { a ( a + 6 ) }$