31) \(\frac{3}{75}+\frac{71}{450}\); \(\frac{21}{27}-\frac{2}{3}\)

\(\frac{3}{75}+\frac{71}{450}=\frac{18}{450}+\frac{71}{450}=\frac{89}{450}\).

\(\frac{21}{27}-\frac{2}{3}=\frac{7}{9}-\frac{6}{9}=\frac{1}{9}\).

Ответ: \(\frac{89}{450};\ \frac{1}{9}\).