в) $$\frac{8:2\frac{2}{5}}{5\frac{1}{4}:7}:\frac{2\frac{1}{7}:\frac{5}{7}}{4:\frac{8}{9}}$$;

Решим пример:

1. $$2\frac{2}{5} = \frac{2 \cdot 5 + 2}{5} = \frac{12}{5}$$;
2. $$5\frac{1}{4} = \frac{5 \cdot 4 + 1}{4} = \frac{21}{4}$$;
3. $$2\frac{1}{7} = \frac{2 \cdot 7 + 1}{7} = \frac{15}{7}$$;
4. $$8 : \frac{12}{5} = \frac{8}{1} : \frac{12}{5} = \frac{8 \cdot 5}{12} = \frac{2 \cdot 5}{3} = \frac{10}{3}$$;
5. $$\frac{21}{4} : 7 = \frac{21}{4} : \frac{7}{1} = \frac{21}{4 \cdot 7} = \frac{3}{4}$$;
6. $$\frac{10}{3} : \frac{3}{4} = \frac{10 \cdot 4}{3 \cdot 3} = \frac{40}{9}$$;
7. $$\frac{15}{7} : \frac{5}{7} = \frac{15 \cdot 7}{7 \cdot 5} = \frac{15}{5} = 3$$;
8. $$4 : \frac{8}{9} = \frac{4 \cdot 9}{8} = \frac{9}{2}$$;
9. $$3 : \frac{9}{2} = \frac{3 \cdot 2}{9} = \frac{2}{3}$$;
10. $$\frac{40}{9} : \frac{2}{3} = \frac{40 \cdot 3}{9 \cdot 2} = \frac{20 \cdot 1}{3 \cdot 1} = \frac{20}{3} = 6\frac{2}{3}$$.

Ответ: $$6\frac{2}{3}$$