Answer
$\sqrt[3]{x^{2}}+4\sqrt[3]{x}-21$
Work Step by Step
Use the FOIL method, along with
$\sqrt[n]{a}\times\sqrt[n]{b}=\sqrt[n]{ab},\qquad$
$\sqrt[n]{a^{n}}=(\sqrt[n]{a})^{n}=a$ (for positive a).
$F:\quad \sqrt[3]{x}\times\sqrt[3]{x}=\sqrt[3]{x^{2}}$
$O:\quad \sqrt[3]{x}\times 7=7\sqrt[3]{x}$
$I:\quad -3\times\sqrt[3]{x}=-3\sqrt[3]{x}$
$L:\quad -3\times 7=-21$
Add the terms (O and I are like terms...)
$...$= $\sqrt[3]{x^{2}}+4\sqrt[3]{x}-21$
