\(10^{n+2}-87.10^n=x.10^n\)
\(\Rightarrow10^n\left(100-87\right)=x.10^n\)
\(\Rightarrow10^n.13=x.10^n\)
\(\Rightarrow x=13.\)
\(10^{n+2}-87.10^n=x.10^n\)
\(\Rightarrow10^n.10^2-87.10^n=x.10^n\)
\(\Rightarrow10^n\left(100-87\right)=x.10^n\)
\(\Rightarrow10^n.13-10^n.x=0\)
\(\Rightarrow10^n\left(13-x\right)=0\)
\(\Rightarrow13-x=0\)
\(\Rightarrow x=13\)