\[\left(\frac{5}{12} + \frac{x}{12}\right) - \frac{4}{12} = \]
\[ = \frac{5 + x - 4}{12} = \frac{1 + x}{12} \]
\[ \left(\frac{4}{18} + \frac{x}{18}\right) + \frac{1}{23} = \frac{4 + x}{18} + \frac{1}{23} \]