2 целых - 3 целых 1/7 х (2целых-1целых9/11) :8/21

Решите задачу:

$2- 3\frac{1}{7}*(2-1 \frac{9}{11} ): \frac{8}{21} =\frac{1}{2} \\ \\ 1) 2-1 \frac{9}{11}=1 \frac{11}{11} -1 \frac{9}{11}= \frac{2}{11} ; \\ 2)3\frac{1}{7}*\frac{2}{11}=\frac{22}{7}*\frac{2}{11}= \frac{2*11}{7}*\frac{2}{11}=\frac{4}{7} ; \\ 3)\frac{4}{7}: \frac{8}{21}=\frac{4}{7}*\frac{21}{8}=\frac{4}{7}*\frac{3*7}{4*2}= \frac{3}{2} =1\frac{1}{2}; \\ 4)2-1\frac{1}{2}=1\frac{2}{2}-1\frac{1}{2}=\frac{1}{2}.$