Find the Product $\left( 4 x ^ { 3 } \right) \left( 3 x ^ { 5 } \right)$

Multiple Choice

Find the product. $\left( 4 x ^ { 3 } \right) \left( 3 x ^ { 5 } \right)$

A) $12 x ^ { 8 }$
B) $12 x ^ { 15 }$
C) $7 x ^ { 8 }$
D) $7 x ^ { 15 }$
E) none of these