а) \(\frac{15}{17}\cdot\frac{34}{63}\); б) \(\frac{9}{40}\cdot\frac{10}{7}\)

\[\frac{15}{17}\cdot\frac{34}{63}=\frac{15\cdot 2}{63}=\frac{30}{63}=\frac{10}{21}.\]

Ответ: \(\frac{10}{21}\).

\[\frac{9}{40}\cdot\frac{10}{7}=\frac{9}{28}.\]

Ответ: \(\frac{9}{28}\).