\frac{6}{13}:3\frac{3}{5}=\frac{6}{13}:\frac{18}{5}=\frac{6}{13}*\frac{5}{18}=\frac{1}{13}*\frac{5}{3}=\frac{5}{39}
1\frac{5}{6}+2\frac{4}{7} =1\frac{35}{42}+2\frac{24}{42}=3\frac{59}{42}=4\frac{17}{42}
(3\frac{2}{3})^2 =3\frac{2}{3}*3\frac{2}{3}=\frac{11}{3}*\frac{11}{3}=\frac{121}{9}= 13\frac{4}{9}
4\frac{6}{7}-2\frac{1}{5}=4\frac{30}{35}-2\frac{7}{35}=2\frac{28}{35}=2\frac{4}{5}=2,8
8\frac{2}{9}-3\frac{5}{8}=8\frac{16}{72}-3\frac{45}{72}=4\frac{43}{72}
\frac{7}{15}*\frac{3}{4}=\frac{7}{5}*\frac{1}{4}=\frac{7}{20}
\frac{4}{7}:\frac{8}{21}=\frac{4}{7}*\frac{21}{8}=\frac{1}{1}*\frac{3}{2}=1\frac{1}{2}
2\frac{2}{3}*1\frac{3}{4}=\frac{8}{3}*\frac{7}{4}=\frac{14}{3}=4\frac{2}{3}