$(-2\frac{5}{9} + 1\frac{20}{21}) : 1\frac{8}{49} - 1\frac{7}{9} : (-6) = (-1\frac{98}{63} + 1\frac{60}{63}) : \frac{57}{49} - \frac{16}{9} : (-6) = -\frac{38}{63} * \frac{49}{57} - \frac{16}{9} * (-\frac{1}{6}) = -\frac{2}{9} * \frac{7}{3} - \frac{8}{9} * (-\frac{1}{3}) = -\frac{14}{27} + \frac{8}{27} = -\frac{6}{27} = -\frac{2}{9}$

$(5\frac{5}{9} - 6,8) : (2\frac{13}{30} - 2\frac{1}{12}) * 3,6 = (5\frac{5}{9} - 6\frac{4}{5}) : (2\frac{26}{60} - 2\frac{5}{60}) * \frac{18}{5} = (5\frac{25}{45} - 6\frac{36}{45}) : \frac{21}{60} * \frac{18}{5} = -1\frac{11}{45} : \frac{7}{20} * \frac{18}{5} = -\frac{56}{45} * \frac{20}{7} * \frac{18}{5} = -\frac{8}{5} * \frac{4}{1} * \frac{2}{1} = -\frac{64}{5} = -12\frac{4}{5}$