Perform the Operation and Write the Result in Standard Form $\left( 8 x ^ { 4 } - 6 \right) - \left( 5 x ^ { 4 } - 4 x - 9 \right)$

Multiple Choice

Perform the operation and write the result in standard form. $\left( 8 x ^ { 4 } - 6 \right) - \left( 5 x ^ { 4 } - 4 x - 9 \right)$

A) $3 x ^ { 4 } - 4 x - 15$
B) $3 x ^ { 4 } + 4 x + 3$
C) $3 x ^ { 8 } + 4 x + 3$
D) $3 x ^ { 8 } - 4 x - 15$
E) $13 x ^ { 8 } - 4 x - 15$