a)
[tex] \frac{6}{10 } \times \frac{10}{9} - \frac{7}{9} \div ( \frac{8}{4} - \frac{1}{4} ) = \\ \frac{60}{90} - \frac{7}{9} \div \frac{7}{4} = \\ \frac{2}{3} - \frac{7}{9} \times \frac{4}{7} = \\ \frac{2}{3} - \frac{4}{9 } = \\ \frac{6}{9} - \frac{4}{9} = \frac{2}{9} [/tex]
