\(\left(x-4\right).\left(x-7\right)=0\)

=> \(\orbr{\begin{cases}x-4=0\\x-7=0\end{cases}}\)=> \(\orbr{\begin{cases}x=4\\x=7\end{cases}}\)

\(B=3+3^2+3^3+.....+3^{2006}\)

\(\Rightarrow3B=3^2+3^3+3^4+.....+3^{2007}\)

\(\Rightarrow2B=3^{2007}-3\)

\(\Rightarrow B=\frac{3^{2007}-3}{2}\)

\(2B+3=3^x\)

\(\Rightarrow2.\frac{3^{2007}-3}{2}+3=3^x\)

\(\Rightarrow3^{2007}-3+3=3^x\)

\(\Rightarrow3^{2007}=3^x\)

\(\Rightarrow x=2007\)

\(0x0=0\)