a) | 9 + 7x | = 3 - 5x
\(\Rightarrow\orbr{\begin{cases}9+7x=3-5x\\9+7x=-\left(3-5x\right)\end{cases}}\)
\(\Rightarrow\orbr{\begin{cases}7x+5x=3-9\\9+7x=-3+5x\end{cases}}\)
\(\Rightarrow\orbr{\begin{cases}12x=-6\\7x-5x=-3-9\end{cases}}\)
\(\Rightarrow\orbr{\begin{cases}x=\frac{-1}{6}\\2x=-12\end{cases}}\)
\(\Rightarrow\orbr{\begin{cases}x=\frac{-1}{6}\\x=-6\end{cases}}\)