\[\frac{3x - 1}{x - 4} - \frac{x - 3}{4 - x} = \frac{A}{x - 4}\]
\[\frac{3x - 1 + x - 3}{x - 4} = \frac{A}{x - 4}\]
\[A = 4x - 4\]
\[Ответ:A = 4x - 4.\]