Verify each option
A
![\sqrt[3]{64}\cdot\sqrt[4]{81}](https://img.qammunity.org/2023/formulas/mathematics/college/peo070sncofhtx49b5fjkqx5z02u85qntg.png)
Remember that
64=4^3
and
81=3^4
substitute
![\sqrt[3]{64}\cdot\sqrt[4]{81}=4\cdot3=12](https://img.qammunity.org/2023/formulas/mathematics/college/avsdpxdtn1m4bymri7bbgrg2mzkyfhtfbj.png)
option A simplification is correct
Option B
we have
![\sqrt[3]{x^3}\cdot\sqrt[3]{x^3y^6}=x\cdot xy^2=x^2y^2](https://img.qammunity.org/2023/formulas/mathematics/college/o8yqqvgi21os3b909mo56xxw58vp646nri.png)
option B simplification is correct
Option C
![\sqrt[3]{x^2y^2}\cdot\sqrt[]{4y^2}=2y\cdot\sqrt[3]{x^2y^2}](https://img.qammunity.org/2023/formulas/mathematics/college/xijuc2slc7stm68k2jjvraeozc60x5euiz.png)
option C simplification is correct
Option D
we have
![\sqrt[4]{9x^4}\cdot\sqrt[4]{16x^4}=\sqrt[4]{144x^8}=2x^2\sqrt[4]{9}=2x^2\sqrt[]{3}](https://img.qammunity.org/2023/formulas/mathematics/college/793hm2icqfdtpycljk9vxjnawxedoq25hb.png)
option D, simplification is not correct
therefore
the answer is option D