Помогите пж очень надо дам 20 баллов

Решите задачу:

$\dfrac{9}{10}+\dfrac{4}{9}:\Big(11-10\dfrac{11}{21}\Big)-1\dfrac{2}{3}=\dfrac{9}{10}+\dfrac{4}{9}:\dfrac{10}{21}-\dfrac{5}{3}=\dfrac{9}{10}+\dfrac{4}{9}\cdot \dfrac{21}{10}-\dfrac{5}{3}=\\\\\\=\dfrac{9}{10}+\dfrac{2\cdot 7}{3\cdot 5}-\dfrac{5}{3}=\dfrac{9}{10}+\dfrac{14}{15}-\dfrac{5}{3}=\dfrac{27+28-50}{30}=\dfrac{5}{30}=\dfrac{1}{6}$