§5. Обыкновенные дроби — Упражнения — 5.380 — стр. 63

\( \frac{25}{45} = \frac{z}{9} \)

\(\frac{5}{9} = \frac{z}{9} \quad \Rightarrow \quad z = 5\).

\( \frac{z}{7} = \frac{36}{42} \)

\(\frac{z}{7} = \frac{6}{7} \quad \Rightarrow \quad z = 6\).

\( \frac{39}{78} = \frac{3}{z} \)

\(\frac{3}{6} = \frac{3}{z} \quad \Rightarrow \quad z = 6\).

\( \frac{7}{z} = \frac{35}{40} \)

\(\frac{7}{z} = \frac{7}{8} \quad \Rightarrow \quad z = 8\).