Answer
Zero-Product Property
Work Step by Step
$\displaystyle \begin{array}{{>{\displaystyle}l}}
\ \ \ \ \ \ \ 3x=0\\
\ \ \ \ \ \ \ 3*x=0\\
And\ since\ 3\neq 0,\ x\ must\ be=0\\
\\
This\ is\ called\ the\ Zero-Product\ Property
\end{array}$