Упростивыражения

1. \(y^{3,4}\cdoty^{−1,8}=\) [ ];
2. \(y^{\frac{15}{28}} : y^{\frac{6}{7}}=\) [ ];
3. \((y^{−4})^{0,9}=\) [ ];
4. \((x^{\frac{10}{21}}y^{\frac{16}{35}})^{\frac{49}{20}}=\) [ ];
5. \({(\sqrt[5]{a^{−4}})}^{\frac{5}{16}}\cdot{(a^{−\frac{7}{8}})}^{\frac{4}{21}}=\) [ ].