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а) $\frac{2}{9}x + \frac{4}{9}x = (\frac{2}{9} + \frac{4}{9})x = \frac{6}{9}x = \frac{2}{3}x$ б) $\frac{5}{7}a - \frac{9}{14}a = (\frac{5}{7} - \frac{9}{14})a = (\frac{10}{14} - \frac{9}{14})a = \frac{1}{14}a$ в) $\frac{7}{12}m - \frac{5}{12}m = (\frac{7}{12} - \frac{5}{12})m = \frac{2}{12}m = \frac{1}{6}m$ г) $\frac{5}{6}b - \frac{3}{4}b = (\frac{5}{6} - \frac{3}{4})b = (\frac{10}{12} - \frac{9}{12})b = \frac{1}{12}b$ д) $3\frac{1}{6}z + 2\frac{2}{3}z = (3\frac{1}{6} + 2\frac{2}{3})z = (3\frac{1}{6} + 2\frac{4}{6})z = (5\frac{5}{6})z = \frac{35}{6}z$ е) $2\frac{3}{4}t - 1\frac{1}{8}t = (2\frac{3}{4} - 1\frac{1}{8})t = (2\frac{6}{8} - 1\frac{1}{8})t = (1\frac{5}{8})t = \frac{13}{8}t$