#### Answer

$a^{3}bc^{5}$

#### Work Step by Step

$\sqrt[4] (a^{12}b^{4}c^{20})=\sqrt[4] (a^{12}\times b^{4}\times c^{20})=\sqrt[4] (a^{12})\times \sqrt[4] (b^{4})\times \sqrt[4] (c^{20})=a^{3}bc^{5}$
$\sqrt[4] (a^{12})=a^{3}$, because $(a^{3})^{4}=a^{3\times4}=a^{12}$
$\sqrt[4] (b^{4})=b$, because $(b)^{4}=b^{4}$
$\sqrt[4] (c^{20})=c^{5}$, because $(c^{5})^{4}=c^{5\times4}=c^{20}$