6) (1/13 - 2 3/4) * 26

6) $$(\frac{1}{13} - 2\frac{3}{4}) \cdot 26 = (\frac{1}{13} - \frac{2 \cdot 4 + 3}{4}) \cdot 26 = (\frac{1}{13} - \frac{11}{4}) \cdot 26 = (\frac{1 \cdot 4}{13 \cdot 4} - \frac{11 \cdot 13}{4 \cdot 13}) \cdot 26 = (\frac{4}{52} - \frac{143}{52}) \cdot 26 = \frac{-139}{52} \cdot 26 = \frac{-139}{2} = -69.5$$

Ответ: -69.5