Calculate $\sqrt[3]{20+14 \sqrt{2}}+\sqrt[3]{20-14 \sqrt{2}}$
Let the original expression $=x$, then $x^{3}=40+6 x$, its positive root $x=4$.

Translate the above text into English, please keep the original text's line breaks and format, and output the translation result directly. 

Let the original expression $=x$, then $x^{3}=40+6 x$, its positive root $x=4$.