Final Answer:
a. \( 15x^4 \sqrt{3x^7} \)
Step-by-step explanation:
To simplify the expression

The expression becomes

Consolidating the constants results in

The expression is

Finally, this can be rewritten as \( 15x^4 \sqrt{3x^7} \), which matches option a.
Hence, the equivalent expression to \
, matching choice a.