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

Multiple Choice

Find the product. $\left( x ^ { 4 n } \right) \left( x ^ { 5 n } \right)$ Assume that the variables in the exponents represent positive integers; for example, $\left( x ^ { 2 n } \right) \left( x ^ { 4 n } \right) = x ^ { 2 n + 4 n } = x ^ { 6 n }$ .

A) $x ^ { 7 n }$
B) $x ^ { 6 n }$
C) $x ^ { 9 n }$
D) $x ^ { 5 n }$
E) $x ^ { 2 n }$