Chapter 7 - Sections 7.1-7.5 - Integrated Review - Radicals and Rational Exponents - Page 447: 23

$3x\sqrt[3] (2x)$

$\sqrt[3] (54x^{4})=\sqrt[3] (27\times x^{3}\times2x)=\sqrt[3] 27\times \sqrt[3] (x^{3})\times\sqrt[3] (2x)=3x\sqrt[3] (2x)$ We know that $\sqrt[3] 27=3$, because $3^{3}=27$. We know that $\sqrt[3] (x^{3})=x$, because $(x)^{3}=x^{3}$.