Find the Cube Root $\sqrt [ 3 ] { - 64 x ^ { 6 } }$

Find the cube root.
- $\sqrt [ 3 ] { - 64 x ^ { 6 } }$

A) $16 x ^ { 2 }$
B) $- 4 x ^ { 2 }$
C) not a real number
D) $8 x ^ { 2 }$