Answer
$\sqrt[12]{125x^4}$
Work Step by Step
Using $a^{m/n}=\sqrt[n]{a^m}$ and the laws of exponents, then,
\begin{array}{l}
\sqrt[4]{5}\cdot\sqrt[3]{x}
\\\\=
5^{\frac{1}{4}}\cdot x^{\frac{1}{3}}
\\\\=
5^{\frac{3}{12}}\cdot x^{\frac{4}{12}}
\\\\=
(5^3\cdot x^4)^{\frac{1}{12}}
\\\\=
(125x^4)^{\frac{1}{12}}
\\\\=
\sqrt[12]{125x^4}
.\end{array}
