$$11\frac{6}{7} + 13\frac{5}{7} = (11+13) + (\frac{6}{7} + \frac{5}{7}) = 24 + \frac{11}{7} = 24 + 1\frac{4}{7} = 25\frac{4}{7}$$
Ответ: $$25\frac{4}{7}$$