\[12 - (4 - x)^{2} = x(3 - x)\]
\[12 - \left( 16 - 8x + x^{2} \right) = 3x - x^{2}\]
\[12 - 16 + 8x - x^{2} + x^{2} - 3x = 0\]
\[5x = 4\]
\[x = \frac{4}{5}\]
\[x = 0,8.\]