Multiply and Simplify $( 2 \sqrt { x } - 9 ) ^ { 2 }$

Multiply and simplify. Assume that all variables represent positive real numbers.
- $( 2 \sqrt { x } - 9 ) ^ { 2 }$

A) $4 x - 36 \sqrt { x } + 81$
B) $4 x + 36 \sqrt { x } + 81$
C) 4x - 45
D) 4x - 81