a) $\frac{7}{2} \times \frac{1}{6} = \frac{7}{{12}}$
b) $\frac{8}{{11}} \times 4 = \frac{{32}}{{11}}$
c) $\frac{8}{9}:\frac{2}{5} = \frac{8}{9} \times \frac{5}{2} = \frac{{40}}{{18}} = \frac{{20}}{9}$
d) $\frac{5}{8}:7 = \frac{5}{8} \times \frac{1}{7} = \frac{5}{{56}}$