Answer:
[tex]\large\boxed{B.\ x^{\frac{9}{4}}}[/tex]
Step-by-step explanation:
[tex]\text{use}\\\\a^\frac{m}{n}=\sqrt[n]{a^m}\\\\a^n\cdot a^m=a^{n+m}\\=================\\\\\left(\sqrt[4]{x^6}\right)\left(\sqrt[12]{x^9}\right)=\left(x^\frac{6}{4}\right)\left(x^\frac{9}{12}\right)=x^{\frac{6}{4}+\frac{9:3}{12:3}}=x^{\frac{6}{4}+\frac{3}{4}}=x^\frac{6+3}{4}=x^{\frac{9}{4}[/tex]
