-3n+9<6n+18

-3n + 9 < 6n + 18

Add 3n to both sides:

         9 < 9n + 18

Subtract 18 from both sides:

        -9 < 9n

Divide both sides by 9:

        -1 < n     or     n > -1

$${\mathtt{\,-\,}}{\mathtt{3}}{n}{\mathtt{\,\small\textbf+\,}}{\mathtt{\,\small\textbf+\,}}{\mathtt{18}} = {\mathtt{\,-\,}}{\mathtt{3}}{n}{\mathtt{\,\small\textbf+\,}}{\mathtt{18}}{\mathtt{\,\small\textbf+\,}}$$