\[\frac{x^{2} - x}{x + 3} = \frac{12}{x + 3};\ \ \ x \neq - 3\]
\[x^{2} - x = 12\]
\[x^{2} - x - 12 = 0\]
\[x_{1} + x_{2} = 1;\ \ x_{1} \cdot x_{2} = - 12\]
\[x_{1} = - 3;\ \ x_{2} = 4.\]
\[Ответ:x = 4.\]