38) $$\frac{5}{6}a + \frac{7}{8} + \frac{7}{12}a - \frac{5}{12} =$$ $$ \frac{5}{6}a + \frac{7}{12}a + \frac{7}{8} - \frac{5}{12} = $$ $$ \frac{5 \cdot 2}{6 \cdot 2}a + \frac{7}{12}a + \frac{7 \cdot 3}{8 \cdot 3} - \frac{5 \cdot 2}{12 \cdot 2} = $$ $$ \frac{10}{12}a + \frac{7}{12}a + \frac{21}{24} - \frac{10}{24} =$$ $$ \frac{17}{12}a + \frac{11}{24}$$
Ответ: $$\frac{17}{12}a + \frac{11}{24}$$