\[f(x) = \frac{x^{2} - 5x + 4}{x - 4},\ \ \ \ \ x \neq 4\]
\[x^{2} - 5x + 4 = 0\]
\[x_{1} + x_{2} = 5,\ \ \ \ \ \ x_{1}{\cdot x}_{2} = 4\]
\[x = 1,\ \ \ \ \]
\[x = 4 - не\ удовлетворяет.\]
\[Ответ:\ x = \ 1.\]