Решение:

а) $$6\frac{1}{3}-8 = \frac{19}{3} - 8 = \frac{19}{3} - \frac{24}{3} = -\frac{5}{3} = -1\frac{2}{3}$$ б) $$-2\frac{2}{7}+4\frac{3}{5} = -\frac{16}{7} + \frac{23}{5} = -\frac{16 \cdot 5}{7 \cdot 5} + \frac{23 \cdot 7}{5 \cdot 7} = -\frac{80}{35} + \frac{161}{35} = \frac{81}{35} = 2\frac{11}{35}$$ в) $$5\frac{1}{3}-6\frac{1}{4} = \frac{16}{3} - \frac{25}{4} = \frac{16 \cdot 4}{3 \cdot 4} - \frac{25 \cdot 3}{4 \cdot 3} = \frac{64}{12} - \frac{75}{12} = -\frac{11}{12}$$ г) $$\frac{3}{8}:(-\frac{9}{16}) = \frac{3}{8} \cdot (-\frac{16}{9}) = -\frac{3 \cdot 16}{8 \cdot 9} = -\frac{3 \cdot 2}{1 \cdot 9} = -\frac{6}{9} = -\frac{2}{3}$$ д) $$\frac{5}{12} \cdot (-6) = -\frac{5 \cdot 6}{12} = -\frac{5 \cdot 1}{2} = -\frac{5}{2} = -2\frac{1}{2}$$ e) $$-3\frac{2}{9} \cdot 3 = -\frac{29}{9} \cdot 3 = -\frac{29 \cdot 3}{9} = -\frac{29 \cdot 1}{3} = -\frac{29}{3} = -9\frac{2}{3}$$ ж) $$\frac{4}{7} \cdot (-49) = -\frac{4 \cdot 49}{7} = -\frac{4 \cdot 7}{1} = -28$$ з) $$-16:(-\frac{4}{9}) = -16 \cdot (-\frac{9}{4}) = \frac{16 \cdot 9}{4} = \frac{4 \cdot 9}{1} = 36$$ и) $$-3\frac{1}{2} \cdot (-1\frac{3}{7}) = -\frac{7}{2} \cdot (-\frac{10}{7}) = \frac{7 \cdot 10}{2 \cdot 7} = \frac{1 \cdot 5}{1 \cdot 1} = 5$$