Решение:

1. а) $$\frac{3}{7} : \frac{7}{9} = \frac{3}{7} \cdot \frac{9}{7} = \frac{3 \cdot 9}{7 \cdot 7} = \frac{27}{49}$$

2. б) $$\frac{5}{28} : \frac{15}{42} = \frac{5}{28} \cdot \frac{42}{15} = \frac{5 \cdot 42}{28 \cdot 15} = \frac{1 \cdot 3}{2 \cdot 3} = \frac{1}{2}$$

3. в) $$\frac{6}{13} : \frac{9}{52} = \frac{6}{13} \cdot \frac{52}{9} = \frac{6 \cdot 52}{13 \cdot 9} = \frac{2 \cdot 4}{1 \cdot 3} = \frac{8}{3} = 2 \frac{2}{3}$$

4. г) $$56 : \frac{7}{8} = 56 \cdot \frac{8}{7} = \frac{56 \cdot 8}{7} = \frac{8 \cdot 8}{1} = 64$$

5. д) $$2 \frac{3}{5} : \frac{13}{20} = \frac{13}{5} : \frac{13}{20} = \frac{13}{5} \cdot \frac{20}{13} = \frac{13 \cdot 20}{5 \cdot 13} = \frac{1 \cdot 4}{1 \cdot 1} = 4$$

6. е) $$3 \frac{3}{4} : 4 \frac{3}{8} = \frac{15}{4} : \frac{35}{8} = \frac{15}{4} \cdot \frac{8}{35} = \frac{15 \cdot 8}{4 \cdot 35} = \frac{3 \cdot 2}{1 \cdot 7} = \frac{6}{7}$$