\[\sqrt[6]{x\sqrt[3]{x}} = \sqrt[6]{\sqrt[3]{x^{3}} \cdot \sqrt[3]{x}} =\]
\[= \sqrt[6]{\sqrt[3]{x^{3} \cdot x}} = \sqrt[6]{\sqrt[3]{x^{4}}} =\]
\[= \sqrt[18]{x^{4}} = \sqrt[9]{x^{2}}\]
\[x = \sqrt{5^{9}}:\]
\[\sqrt[9]{\left( \sqrt{5^{9}} \right)^{2}} = \sqrt[9]{5^{9}} = 5.\]