Write the Expression with Only Positive Exponents and Evaluate If $( 3 x ) ^ { - 2 }$

Multiple Choice

Write the expression with only positive exponents and evaluate if possible. Assume all variables represent nonzero real
numbers.
- $( 3 x ) ^ { - 2 }$

A) $- 9 x ^ { 2 }$
B) $\frac { 1 } { 9 x ^ { 2 } }$
C) $- \frac { 1 } { 6 x }$
D) $- 6 x$