a cube, will be like the one in the picture below, with all equal sides, and therefore with a volume of x³.
[tex]\bf \textit{volume of a cube}\\\\
V=x^3~~
\begin{cases}
x=side's~length\\[-0.5em]
\hrulefill\\
V=343
\end{cases}\implies 343=x^3\implies \sqrt[3]{343}=x\implies 7=x[/tex]
