Simplify the Exponential Expression $$36 ^ { - 3 / 2 }$$

Multiple Choice

Simplify the exponential expression. Write any negative exponents as positive exponents. Assume all variables represent positive real numbers.
- $$36 ^ { - 3 / 2 }$$

A) $\frac { 1 } { 216 }$
B) $- \frac { 1 } { 216 }$
C) $- 216$
D) 216