Let [tex]s=[/tex] the length of a side of the sign
We get [tex]s-2=[/tex] the length of a side of the poster
Difference between areas is 52
So [tex]s^{2}-(s-2)^{2}=52[/tex]
⇒[tex]s^{2}-(s^{2}-4s+4)=52[/tex]
⇒[tex]4s-4=52[/tex]
⇒[tex]4s=56[/tex]
⇒[tex]s=14[/tex] is the length of a side of the sign
Plug into [tex]s-2=14-2=12[/tex] is the length of a side of the poster