Add the Polynomials $\left( 6 x ^ { 2 } - 3 x + 8 \right) + \left( 3 x ^ { 2 } - 3 x - 2 \right)$

Multiple Choice

Add the polynomials.
- $\left( 6 x ^ { 2 } - 3 x + 8 \right) + \left( 3 x ^ { 2 } - 3 x - 2 \right)$

A) $9 x ^ { 4 } - 6 x ^ { 2 } + 6$
B) $9 x ^ { 2 } - 3 x + 6$
C) $18 x ^ { 2 } - 3 x + 6$
D) $9 x ^ { 2 } - 6 x + 6$