Simplify the Expression $6 \sqrt { 48 x ^ { 2 } } - 2 \sqrt { 27 x ^ { 2 } } - \sqrt { 3 x ^ { 2 } }$

Multiple Choice

Simplify the expression. Assume all variables represent positive real numbers.
- $6 \sqrt { 48 x ^ { 2 } } - 2 \sqrt { 27 x ^ { 2 } } - \sqrt { 3 x ^ { 2 } }$

A) $17 x \sqrt { 3 }$
B) $4 x \sqrt { 21 }$
C) $3 x \sqrt { 21 }$
D) $18 x \sqrt { 3 }$