Ответ:

\(\frac{3}{5}-\frac{8}{15}=\frac{9}{15}-\frac{8}{15}=\frac{1}{15}\).

\(\frac{13}{900}-\frac{7}{450}=\frac{13}{900}-\frac{14}{900}=-\frac{1}{900}\).

Ответ: \(\frac{1}{15};\ -\frac{1}{900}\).