\[ -8\frac{11}{12} = -\frac{8 \times 12 + 11}{12} = -\frac{96 + 11}{12} = -\frac{107}{12} \]
\[ -\frac{107}{12} + \frac{13}{18} \]
Найдем общий знаменатель для 12 и 18. НОК(12, 18) = 36.
\[ -\frac{107 \times 3}{12 \times 3} + \frac{13 \times 2}{18 \times 2} = -\frac{321}{36} + \frac{26}{36} = \frac{-321 + 26}{36} = \frac{-295}{36} \]
\[ -6 - \left(-\frac{295}{36}\right) = -6 + \frac{295}{36} \]
Приведем -6 к знаменателю 36:
\[ -6 = -\frac{6 \times 36}{36} = -\frac{216}{36} \]
\[ -\frac{216}{36} + \frac{295}{36} = \frac{-216 + 295}{36} = \frac{79}{36} \]
Ответ: \(\frac{79}{36}\).