Choose the One Alternative That Best Completes the Statement or Answers

Multiple Choice

Choose the one alternative that best completes the statement or answers the question.
Simplify. Assume that all variables represent positive real numbers.
- $3 \sqrt[3]{8 x}+3 \sqrt[3]{64 x}$

A) $18 x$
B) $3 \sqrt[3]{72 x}$
C) $6 \sqrt[3]{x}$
D) $18 \sqrt[3]{x}$