г) $$\frac{5}{6} - \frac{4}{9} * \frac{16}{21} =$$

$$\frac{5}{6} - \frac{4}{9} * \frac{16}{21} = \frac{5}{6} - \frac{64}{189} = \frac{5 * 63}{6 * 63} - \frac{64 * 2}{189 * 2} = \frac{315 - 128}{378} = \frac{187}{378}$$

Ответ: $$\frac{187}{378}$$