4. Решите уравнения: a) x - 5 3/8 = 7 1/8; б) 1/7 * x = 4 3/7; в) 7/12 : x = 2/3

a) \(x - 5 \frac{3}{8} = 7 \frac{1}{8}\)
\(x = 7 \frac{1}{8} + 5 \frac{3}{8}\)
\(x = 12 \frac{4}{8}\)
\(x = 12 \frac{1}{2}\)

б) \( \frac{1}{7} x = 4 \frac{3}{7} \)
\( \frac{1}{7} x = \frac{31}{7} \)
\( x = \frac{31}{7} \cdot 7 \)
\( x = 31 \)

в) \( \frac{7}{12} : x = \frac{2}{3} \)
\( x = \frac{7}{12} : \frac{2}{3} \)
\( x = \frac{7}{12} \cdot \frac{3}{2} \)
\( x = \frac{7 \cdot 3}{12 \cdot 2} \)
\( x = \frac{7 \cdot 3}{4 \cdot 3 \cdot 2} \)
\( x = \frac{7}{8} \)

Ответ:
a) \(x = 12 \frac{1}{2}\)
б) \(x = 31\)
в) \(x = \frac{7}{8}\)