a) $\frac{-5}{6}\;:\;\frac{2}{7} = \frac{-5}{6}\times \frac{7}{2} = \frac{-35}{12}$

b) $\frac{-7}{8}\;:\;\frac{-1}{4} = \frac{-7}{8}\times (-4) = \frac{7}{2}$

c) $12\;:\;\frac{6}{7} = 12\times \frac{7}{6} = 14$

d) $\frac{1}{15}\;:\;\frac{-3}{5} = \frac{1}{15}\times \frac{-5}{3} = \frac{-1}{9}$

e) $0\;:\;\frac{-5}{36} = 0\times \frac{-36}{5} = 0$

f) $\frac{7}{9}\;:\;(-7) = \frac{7}{9}\times \frac{-1}{7} = \frac{-1}{9}$