distribute the 3 in the parentheses
[tex]27=3x-18+6x[/tex]simplify common factors
[tex]27=9x-18[/tex]add 18 on both sides and simplify
[tex]\begin{gathered} 27+18=9x-18+18 \\ 45=9x \end{gathered}[/tex]divide by 9 on both sides
[tex]\begin{gathered} \frac{45}{9}=x \\ 5=x \end{gathered}[/tex]