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