\(3^x\times\left(3^2-1\right)=216\)
\(3^x\times\left(9-1\right)=216\)
\(3^x\times8=216\)
\(3^x=\frac{216}{8}\)
\(3^x=27\)
\(3^x=3^3\)
\(x=3\)
\(6^x=8\times3^x\)
\(\frac{6^x}{3^x}=8\)
\(\left(\frac{6}{3}\right)^x=2^3\)
\(2^x=2^3\)
\(x=3\)
\(\left(3x+1\right)^3=1\)
\(3x+1=1\)
\(3x=1-1\)
\(3x=0\)
\(x=0\)