B) z- =; 21 г) -k=, 20 8 11 21 21 7 1 20 20

в) Решим уравнение:

$$z - \frac{8}{21} = \frac{11}{21}$$ $$z = \frac{11}{21} + \frac{8}{21}$$ $$z = \frac{11 + 8}{21}$$ $$z = \frac{19}{21}$$

Ответ: $$z = \frac{19}{21}$$

г) Решим уравнение:

$$\frac{7}{20} - k = \frac{1}{20}$$ $$k = \frac{7}{20} - \frac{1}{20}$$ $$k = \frac{7 - 1}{20}$$ $$k = \frac{6}{20}$$ $$k = \frac{3}{10}$$

Ответ: $$k = \frac{3}{10}$$