4) (2\frac{7}{10} - 1\frac{8}{15})^2 \cdot \frac{9}{14}

4)

$$(2\frac{7}{10} - 1\frac{8}{15})^2 \cdot \frac{9}{14} = (\frac{27}{10} - \frac{23}{15})^2 \cdot \frac{9}{14} = (\frac{27 \cdot 3}{10 \cdot 3} - \frac{23 \cdot 2}{15 \cdot 2})^2 \cdot \frac{9}{14} =$$

$$=(\frac{81}{30} - \frac{46}{30})^2 \cdot \frac{9}{14} = (\frac{35}{30})^2 \cdot \frac{9}{14} = (\frac{7}{6})^2 \cdot \frac{9}{14} = \frac{49}{36} \cdot \frac{9}{14} = \frac{7}{4} \cdot \frac{1}{2} = \frac{7}{8}$$

Ответ: $$\frac{7}{8}$$