Answer
$3x+8$
Work Step by Step
Using $a^3\pm b^3=(a\pm b)(a^2\mp ab+b^2)$, then,
\begin{array}{l}
\left( \sqrt[3]{3x}+2 \right)\left( \sqrt[3]{9x^2}-2\sqrt[3]{3x}+4 \right)
\\=
(\sqrt[3]{3x})^3+(2)^3
\\=
3x+8
.\end{array}
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