6. Найдите значение выражения: $$\frac{9}{10} + \frac{4}{9} : (2 - 1\frac{11}{21}) - 1\frac{2}{3}$$

$$\frac{9}{10} + \frac{4}{9} : (2 - 1\frac{11}{21}) - 1\frac{2}{3} = \frac{9}{10} + \frac{4}{9} : (\frac{42}{21} - \frac{32}{21}) - \frac{5}{3} = \frac{9}{10} + \frac{4}{9} : \frac{10}{21} - \frac{5}{3} = \frac{9}{10} + \frac{4}{9} * \frac{21}{10} - \frac{5}{3} = \frac{9}{10} + \frac{4*21}{9*10} - \frac{5}{3} = \frac{9}{10} + \frac{2*7*3*2}{3*3*2*5} - \frac{5}{3} = \frac{9}{10} + \frac{14}{15} - \frac{5}{3} = \frac{27}{30} + \frac{28}{30} - \frac{50}{30} = \frac{55}{30} - \frac{50}{30} = \frac{5}{30} = \frac{1}{6}$$ Ответ: $$\frac{1}{6}$$