Пошаговое объяснение:

8/15 : (-4/5) = 8/15 * (-5/4) = -40/60 = -2/3

12 : (-6/7) = 12 * (-7/6) = 2 * (-7/1) = -14/1 = -14

-1 5/7 : (-15/4) = -12/7 * (-4/15) = -4/7 * (-4/5) = 16/35