\(\Leftrightarrow12^x-8.4^x-3.3^x+24=0\)
\(\Leftrightarrow4^x\left(3^x-8\right)-3\left(3^x-8\right)=0\)
\(\Leftrightarrow\left(4^x-3\right)\left(3^x-8\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}4^x=3\\3^x=8\end{matrix}\right.\)
\(\Rightarrow\left[{}\begin{matrix}x=log_43\\x=log_38\end{matrix}\right.\)
\(\Rightarrow log_43.log_38=\dfrac{3}{2}\)