Add or Subtract $18 \sqrt [ 3 ] { 2 } - 3 \sqrt [ 3 ] { 54 }$

Multiple Choice

Add or subtract. Assume all variables represent positive real numbers.
- $18 \sqrt [ 3 ] { 2 } - 3 \sqrt [ 3 ] { 54 }$

A) $15 \sqrt [ 3 ] { 2 }$
B) $18 \sqrt [ 3 ] { 2 } - 3 \sqrt [ 3 ] { 54 }$
C) $9 \sqrt [ 3 ] { 2 }$
D) $- 9 \sqrt [ 3 ] { 2 }$