Simplify the Expression by Using the Properties of Rational Exponents $$\left( \frac { 81 s ^ { 12 } r ^ { - 4 } } { 16 s ^ { - 4 } r ^ { 4 } } \right) ^ { 3 / 4 }$$

Multiple Choice

Simplify the expression by using the properties of rational exponents. Write the final answer using positive exponents only. $$\left( \frac { 81 s ^ { 12 } r ^ { - 4 } } { 16 s ^ { - 4 } r ^ { 4 } } \right) ^ { 3 / 4 }$$

A) $\frac { 3 s ^ { 12 } } { 2 r ^ { 6 } }$
B) $\frac { 27 s ^ { 6 } } { 8 }$
C) $\frac { 3 s ^ { 16 } r ^ { 8 } } { 2 }$
D) $\frac { 27 s ^ { 12 } } { 8 r ^ { 6 } }$