Answer
$\frac{24-6\sqrt{3a}}{16-3a}$.
Work Step by Step
The given expression is
$=\frac{6}{4+\sqrt{3a}}$
Multiply and divide by the conjugate of the denominator.
$=\frac{6}{4+\sqrt{3a}}\cdot \frac{4-\sqrt{3a}}{4-\sqrt{3a}}$
Use distributive property and the FOIL method.
$=\frac{24-6\sqrt{3a}}{16-4\sqrt{3a}+4\sqrt{3a}+(\sqrt{3a})(-\sqrt{3a})}$
Simplify.
$=\frac{24-6\sqrt{3a}}{16-3a}$.