Answer :

naǫ
[tex]a+18=7a \ \ \ |\hbox{subtract 7a from both sides} \\ -6a+18=0 \ \ \ |\hbox{subtract 18 from both sides} \\ -6a=-18 \ \ \ |\hbox{divide both sides by (-6)} \\ a=3[/tex]
ValyRemus
[tex]a+18=7a[/tex]

[tex]18=7a-a[/tex]

[tex]18=6a[/tex] ⇒ [tex]a= \frac{18}{6} [/tex]

[tex]\boxed {a=3}[/tex]