Ответ:

\[\sqrt{\frac{9}{64}}=\frac{3}{8},\qquad \sqrt{\frac{49}{100}}=\frac{7}{10}.\]

\[\frac{3}{8}-\frac{7}{10}=\frac{15}{40}-\frac{28}{40}=-\frac{13}{40}.\]

Ответ: \(-\frac{13}{40}\).