Найдите значение выражения: a) $$(\frac{2}{3} + \frac{4}{7}) \cdot 42$$; б) $$(2\frac{1}{4} - 1\frac{1}{2}) \cdot 8$$; в) $$4\frac{1}{6} \cdot 3\frac{2}{7} + 2\frac{5}{7} \cdot 4\frac{1}{6}$$.

a) $$(\frac{2}{3} + \frac{4}{7}) \cdot 42 = (\frac{14}{21} + \frac{12}{21}) \cdot 42 = \frac{26}{21} \cdot 42 = \frac{26 \cdot 42}{21} = \frac{26 \cdot 2}{1} = 52$$

б) $$(2\frac{1}{4} - 1\frac{1}{2}) \cdot 8 = (\frac{9}{4} - \frac{3}{2}) \cdot 8 = (\frac{9}{4} - \frac{6}{4}) \cdot 8 = \frac{3}{4} \cdot 8 = \frac{3 \cdot 8}{4} = 3 \cdot 2 = 6$$

в) $$4\frac{1}{6} \cdot 3\frac{2}{7} + 2\frac{5}{7} \cdot 4\frac{1}{6} = \frac{25}{6} \cdot \frac{23}{7} + \frac{19}{7} \cdot \frac{25}{6} = \frac{25}{6} \cdot (\frac{23}{7} + \frac{19}{7}) = \frac{25}{6} \cdot \frac{42}{7} = \frac{25}{6} \cdot 6 = 25$$