\(99-\left(56-3x\right)\div3=96\)
\(\Leftrightarrow\left(56-3x\right)\div3=99-96\)
\(\Leftrightarrow\left(56-3x\right)\div3=3\)
\(\Leftrightarrow56-3x=3.3\)
\(\Leftrightarrow56-3x=9\)
\(\Leftrightarrow3x=56-9\)
\(\Leftrightarrow3x=47\)
\(\Leftrightarrow x=\frac{47}{3}\)