a) $A = 11\frac{3}{13} - (3\frac{4}{7} + 6\frac{3}{13}) = (11\frac{3}{13} - 6\frac{3}{13}) - 3\frac{4}{7} = 5 - \frac{25}{7} = \frac{35}{7} - \frac{25}{7} = \frac{10}{7} = 1\frac{3}{7}$

b) $B = (7\frac{4}{9} + 3\frac{8}{13}) - 5\frac{4}{9} = (7\frac{4}{9} - 5\frac{4}{9}) + 3\frac{8}{13} = 2 + \frac{47}{13} = \frac{26}{13} + \frac{47}{13} = \frac{73}{13} = 5\frac{8}{13}$.

c) $C = \frac{-2}{7}\times \frac{5}{11} + \frac{-2}{7}\times \frac{6}{11} + 5\frac{4}{7} = \frac{-2}{7}\times (\frac{5}{11} + \frac{6}{11}) + 5\frac{4}{7} = \frac{-2}{7} + \frac{39}{7} = \frac{37}{7} = 5\frac{2}{7}$;

d) $D = 0,7\times 1\frac{3}{5}\times 30 \times 0,375\times \frac{4}{7} = \frac{7}{10}\times \frac{8}{5}\times 30 \times \frac{3}{8}\times \frac{4}{7} = 30 \times \frac{7}{10}\times \frac{4}{7}\times \frac{8}{5}\times \frac{3}{8} = 24$