Ответ:
\[\frac{13}{21}-\frac{3}{7}=\frac{13}{21}-\frac{9}{21}=\frac{4}{21}.\]
\[\frac{7}{12}\cdot\frac{4}{21}=\frac{1}{3}\cdot\frac{1}{3}=\frac{1}{9}.\]
Ответ: \(\frac{1}{9}\)
\[\frac{13}{21}-\frac{3}{7}=\frac{13}{21}-\frac{9}{21}=\frac{4}{21}.\]
\[\frac{7}{12}\cdot\frac{4}{21}=\frac{1}{3}\cdot\frac{1}{3}=\frac{1}{9}.\]
Ответ: \(\frac{1}{9}\)