REPEDE!!!! DAU COROANA!!! PANA LA ORA 20:30

Răspuns:
[tex]a \: \: \: \frac{1}{7} + \frac{3}{7} \\b \: \: \: \: \frac{6}{7} - \frac{2}{7} \\ c \: \: \: \frac{1}{7} + \frac{2}{7} + \frac{1}{7} [/tex]