\[\boxed{\text{420\ (420).}\text{\ }\text{Еуроки\ -\ ДЗ\ без\ мороки}}\]
\[\textbf{а)}\ \frac{4x - 1}{12} + \frac{7}{4} = \frac{5 - x}{9}\text{\ \ \ \ }| \cdot 36\]
\[3(4x - 1) + 9 \cdot 7 = 4(5 - x)\]
\[12x - 3 + 63 = 20 - 4x\]
\[16x = - 40\]
\[x = - \frac{40}{16} = - \frac{10}{4}\]
\[x = - 2,5.\]
\[Ответ:x = - 2,5.\]
\[\textbf{б)}\ \frac{2x - 9}{6} - \frac{2(5x + 3)}{15} = \frac{1}{2}\ \ \ \ \ | \cdot 30\]
\[5(2x - 9) - 4(5x + 3) = 15\]
\[10x - 45 - 20x - 12 = 15\]
\[- 10x = 72\]
\[x = 72\ :( - 10)\]
\[x = - 7,2.\]
\[Ответ:x = - 7,2.\]