Resposta:

[tex] \tt{}S = \left\{ 2\right\}[/tex]

Explicação passo-a-passo:

[tex] \tt{}2x + 5 + x + 7 = 18[/tex]

[tex] \tt{}3x + 5 + 7 = 18[/tex]

[tex] \tt{}3x + 12 = 18[/tex]

[tex] \tt{}3x = 18 - 12[/tex]

[tex] \tt{}3x = 6[/tex]

[tex] \tt{}x = \cfrac{6}{3} [/tex]

Solução:

[tex] \tt{}x = 2[/tex]

[tex]\begin{gathered}\rule{07cm}{0.15mm}\\\texttt{Bons estudos!}\\\rule{7cm}{0.15mm}\end{gathered}[/tex]

[tex]\huge \orange\star \mathscr{{Attard}} \purple\star[/tex]