$-3x\div\left( -3 \right) < 3\div\left( -3 \right)$
Any expression divided by itself equals $1$$x < 3\div\left( -3 \right)$
Dividing a positive and a negative equals a negative: $\left( + \right)\div\left( - \right)=\left( - \right)$$x < -3\div3$
Calculate the quotient$\begin{align*}&x < -1 \\&\begin{array} { l }x \in \langle-\infty, -1\rangle\end{array}\end{align*}$