Ответ:

\[\frac{9}{10}-\frac{3}{5}=\frac{9}{10}-\frac{6}{10}=\frac{3}{10}.\]

\[\frac{7}{12}\cdot\frac{9}{14}=\frac{3}{8}.\]

\[\frac{3}{10}:\frac{3}{8}=\frac{3}{10}\cdot\frac{8}{3}=\frac{4}{5}.\]

Ответ: \(\frac{4}{5}\)