19 5 21 6

6) $$\frac{19}{21} - \frac{5}{6} = \frac{19 \cdot 2}{21 \cdot 2} - \frac{5 \cdot 7}{6 \cdot 7} = \frac{38}{42} - \frac{35}{42} = \frac{38-35}{42} = \frac{3}{42} = \frac{1}{14}$$

Ответ: $$\frac{1}{14}$$