Решение:
а) $(-\frac{1}{7}) * \frac{8}{9} * 1\frac{3}{4} = (-\frac{1}{2}) * \frac{8}{9} * \frac{7}{4} = -\frac{1 * 8 * 7}{7 * 9 * 4} = -\frac{1 * 2 * 1}{1 * 9 * 1} = -\frac{2}{9} = -\frac{8}{36}$,
$\frac{2}{-3} * 2\frac{1}{4} * \frac{1}{6} = \frac{2}{-3} * \frac{9}{4} * \frac{1}{6} = -\frac{2 * 9 * 1}{3 * 4 * 6} = -\frac{1 * 1 * 1}{1 * 4 * 1} = -\frac{1}{4} = -\frac{9}{36}$,
$-\frac{8}{36} > -\frac{9}{36};$
б) $(\frac{7}{12} - \frac{7}{18}) * (-\frac{6}{7}) = \frac{21 - 14}{36} * (-\frac{6}{7}) = \frac{7}{36} * (-\frac{6}{7}) = -\frac{1}{6} = -\frac{33}{198}$,
$(-\frac{25}{36}) : \frac{5}{-12} * \frac{-1}{11} = (-\frac{25}{36}) * \frac{-12}{5} * \frac{-1}{11} = -\frac{25 * 12 * 1}{36 * 5 * 11} = -\frac{5 * 1 * 1}{3 * 1 * 11} = -\frac{5}{33} = -\frac{30}{198}$,
$-\frac{33}{198} < -\frac{30}{198}$.