Выполните вычитание: a) $$2 - \frac{1}{3}$$; б) $$3\frac{6}{7} - 2\frac{8}{9}$$

a) $$2 - \frac{1}{3} = \frac{6}{3} - \frac{1}{3} = \frac{5}{3} = 1\frac{2}{3}$$
б) $$3\frac{6}{7} - 2\frac{8}{9} = \frac{27}{7} - \frac{26}{9} = \frac{27 \cdot 9 - 26 \cdot 7}{63} = \frac{243 - 182}{63} = \frac{61}{63}$$