7) (9/14 − (−5/21)) : (−2 9/14);

\(\frac{9}{14}-\left(-\frac{5}{21}\right)=\frac{27}{42}+\frac{10}{42}=\frac{37}{42}\).

\(-2\frac{9}{14}=-\frac{37}{14}\).

\(\frac{37}{42}:\left(-\frac{37}{14}\right)=\frac{37}{42}\cdot\left(-\frac{14}{37}\right)=-\frac{1}{3}\).

Ответ: \(-\frac{1}{3}\).