$a)5\frac{5}{7}+3\frac{4}{7}=8\frac{9}{7}=9\frac{2}{7}$

$b)3\frac{15}{20}+1\frac{9}{20}=4\frac{24}{20}=5\frac{4}{20}=5\frac{1}{5}$

$c)4\frac{4}{9}+5\frac{6}{9}=9\frac{10}{9}=10\frac{1}{9}$

$d)8\frac{7}{10}+3\frac{9}{10}=11\frac{16}{10}=12\frac{6}{10}=12\frac{3}{5}$