Answer:
[tex]\large\boxed{27\sqrt[4]{x^3}}[/tex]
Step-by-step explanation:
[tex]\sqrt[n]{a^m}=a^\frac{m}{n}\\\\(ab)^n=a^nb^n\\\\\sqrt[n]{a^n}=a\\\\\sqrt[n]{ab}=\sqrt[n]{a}\cdot\sqrt[n]{b}\\--------------------\\\\(81x)^\frac{3}{4}=\sqrt[4]{(81x)^3}=\sqrt[4]{81^3x^3}=\sqrt[4]{81^3}\cdot\sqrt[4]{x^3}=\sqrt[4]{(3^4)^3}\cdot\sqrt[4]{x^3}\\\\=\sqrt[4]{(3^3)^4}\cdot\sqrt[4]{x^3}=3^3\sqrt[4]{x^3}=27\sqrt[4]{x^3}[/tex]
