[tex]\bold{a)} \ 6\frac{1}{4}+15\frac{3}{7}=\frac{25}{4}+\frac{108}{7}=\frac{175+432}{28}=\frac{607}{28}=\boxed{21\frac{19}{28}}; \\ \bold{b)} \ 8\frac{1}{2}-12\frac{1}{5}=\frac{17}{2}-\frac{61}{5}=\frac{85-122}{10}=-\frac{37}{10}=\boxed{-3\frac{7}{10}}; \\ \bold{c)} \ 36\frac{1}{3}+15\frac{4}{7}=\frac{109}{3}+\frac{109}{7}=\frac{763+327}{21}=\frac{1 \ 090}{21}=\boxed{51\frac{19}{21}}; \\ \bold{d)} \ 8\frac{1}{9}+18\frac{5}{9}=\frac{73}{9}+\frac{167}{9}=\frac{240}{9}=\frac{80}{3}=\boxed{26\frac{2}{3}};[/tex]
