д) $$\frac{2}{7}$$c + $$\frac{2}{3}$$c - $$\frac{11}{21}$$c = 0

д) $$\frac{2}{7}$$c + $$\frac{2}{3}$$c - $$\frac{11}{21}$$c = 0

$$\frac{6}{21}$$c + $$\frac{14}{21}$$c - $$\frac{11}{21}$$c = 0

$$\frac{9}{21}$$c = 0

$$\frac{3}{7}$$c = 0

c = 0

Ответ: 0