\[\boxed{\text{228\ (228).\ }\text{Еуроки\ -\ ДЗ\ без\ мороки}}\]
\[= \frac{2m^{2}n - 2n}{m^{2} - n^{2}}\ \]
\[\textbf{б)}\ \frac{x + 4a}{3a + 3x} - \frac{a - 4x}{3a - 3x} =\]
\[= \frac{x + 4a^{\backslash a - x}}{3(a + x)} - \frac{a - 4x^{\backslash a + x}}{3(a - x)} =\]
\[= \frac{3(a^{2} + x^{2})}{3(a^{2} - x^{2})} = \frac{a^{2} + x^{2}}{a^{2} - x^{2}}\ \]