\[ 4 - 2\frac{26}{27} = 4 - \frac{80}{27} = \frac{4 \cdot 27}{27} - \frac{80}{27} = \frac{108}{27} - \frac{80}{27} = \frac{28}{27} \]
\[ \frac{8}{15} : \frac{28}{27} = \frac{8}{15} \cdot \frac{27}{28} = \frac{8 \cdot 27}{15 \cdot 28} = \frac{2 \cdot 9}{5 \cdot 7} = \frac{18}{35} \]
\[ \frac{11}{14} + \frac{18}{35} = \frac{11 \cdot 5}{14 \cdot 5} + \frac{18 \cdot 2}{35 \cdot 2} = \frac{55}{70} + \frac{36}{70} = \frac{55+36}{70} = \frac{91}{70} = \frac{13}{10} \]
\[ \frac{13}{10} - 1\frac{1}{10} = \frac{13}{10} - \frac{11}{10} = \frac{13-11}{10} = \frac{2}{10} = \frac{1}{5} \]
Ответ: \(\frac{1}{5}\)