Ответ: \(-2\frac{1}{4}\)
\[\frac{5}{12} - \frac{7}{8} = \frac{5 \cdot 2}{12 \cdot 2} - \frac{7 \cdot 3}{8 \cdot 3} = \frac{10}{24} - \frac{21}{24} = -\frac{11}{24}\]
\[\frac{11}{20} : \left(-\frac{11}{24}\right) = \frac{11}{20} \cdot \left(-\frac{24}{11}\right) = -\frac{11 \cdot 24}{20 \cdot 11} = -\frac{24}{20} = -\frac{6}{5} = -1\frac{1}{5}\]
\[3 \cdot 1\frac{7}{15} = 3 \cdot \frac{1 \cdot 15 + 7}{15} = 3 \cdot \frac{22}{15} = \frac{3 \cdot 22}{15} = \frac{66}{15} = \frac{22}{5} = 4\frac{2}{5}\]
\[-1\frac{1}{5} + 4\frac{2}{5} = -\frac{6}{5} + \frac{22}{5} = \frac{-6 + 22}{5} = \frac{16}{5} = 3\frac{1}{5}\]
Ответ: \(3\frac{1}{5}\)