Решение:

a) $$\frac{7}{9} : (-\frac{1}{36}) = \frac{7}{9} * (-36) = -\frac{7 * 36}{9} = -7 * 4 = -28$$

б) $$\frac{24}{49} : \frac{6}{7} + \frac{1}{14} = \frac{24}{49} * \frac{7}{6} + \frac{1}{14} = \frac{24 * 7}{49 * 6} + \frac{1}{14} = \frac{4}{7} + \frac{1}{14} = \frac{8}{14} + \frac{1}{14} = \frac{9}{14}$$