6-2\frac{2}{7}
3\frac{4}{9}-1\frac{5}{6}
6-2\frac{2}{7}=3\frac{5}{7}
3\frac{4}{9}-1\frac{5}{6}=3\frac{8}{18}-1\frac{15}{18}=
=2\frac{26}{18}-1\frac{15}{18}=1\frac{11}{18}