Вычеслите а)2/3+1/6 б)-1/3+2/5 в)-7/9+1/6

Решите задачу:

$1) \frac{2}{3} + \frac{1}{6} = \frac{2*2}{3*2} + \frac{1}{6} = \frac{4}{6} + \frac{1}{6} = \frac{5}{6} \\ \\ 2)- \frac{1}{3} + \frac{2}{5} = \frac{2}{5} - \frac{1}{3} = \frac{2*3}{5*3} - \frac{1*5}{3*5} = \frac{6-5}{15} = \frac{1}{15} \\ \\ 3)- \frac{7}{9} + \frac{1}{6} = \frac{1}{6} - \frac{7}{9} = \frac{1*6}{6*6} - \frac{7*4}{9*4} = \frac{6}{36} - \frac{28}{36} =- \frac{22}{36} =- \frac{11}{18}$