Simplify the Algebraic Expression $$- 15 x ^ { 3 } - 12 x ^ { 3 }$$

Multiple Choice

Simplify the algebraic expression.
- $$- 15 x ^ { 3 } - 12 x ^ { 3 }$$

A) $- 27 x ^ { 9 }$
B) $- 27 x 6$
C) $- 28 x ^ { 3 }$
D) $- 27 x ^ { 3 }$