\[\boxed{\mathbf{3.21}\mathbf{.\ ОК\ ГДЗ - домашка\ на\ }5}\]
\[\textbf{а)}\ \frac{1}{3} \cdot 2 = \frac{2}{3}\ :\frac{1}{2} = \frac{2}{3} \cdot 2 = \frac{4}{3} =\]
\[= 1\frac{1}{3} - 1\frac{1}{5} = \frac{5}{15} - \frac{3}{15} = \frac{2}{15}\]
\[\textbf{б)}\ 6\ :9 = \frac{6}{9} = \frac{2}{3} + \frac{1}{4} =\]
\[= \frac{8}{12} + \frac{3}{12} = \frac{11}{12} \cdot \frac{12}{11} = 1\ :1\frac{4}{7} =\]
\[= 1\ :\frac{11}{7} = \frac{7}{11} \cdot 9\frac{3}{7} = \frac{7}{11} \cdot \frac{66}{7} = 6\]