\[12 \cdot (2x + 1) - 3 \cdot \left( 4x - x^{2} \right) =\]
\[= 4 \cdot \left( x^{2} - 4 \right)\]
\[24x + 12 - 12x + 3x^{2} - 4x^{2} + 16 = 0\]
\[- x² + 12x + 28 = 0\ \ \ \ \ \ \ \ | \cdot ( - 1)\]
\[x^{2} - 12x - 28 = 0\]
\[x_{1} + x_{2} = 12\]
\[x_{1} \cdot x_{2} = - 28 \Longrightarrow x_{1} = 14;\ \ \]
\[x_{2} = - 2\]
\[Ответ:\ \ x = 14\ \ \ \ и\ \ \ x = - 2.\]