* \(\dfrac{-15}{8}-\dfrac{4}{9}+\dfrac{-1}{8}+\dfrac{-5}{7}+\dfrac{-5}{9}=\dfrac{-15}{8}-\dfrac{4}{9}-\dfrac{1}{8}-\dfrac{5}{7}-\dfrac{5}{9}\)

\(=\left(\dfrac{-15}{8}-\dfrac{1}{8}\right)+\left(\dfrac{-4}{9}-\dfrac{5}{9}\right)-\dfrac{5}{7}=\dfrac{-16}{8}+\dfrac{-9}{9}-\dfrac{5}{7}\)

\(=-2-1-\dfrac{5}{7}=-3-\dfrac{5}{7}=\dfrac{-26}{7}\)

* \(\left(\dfrac{-3}{4}\right)^3-\left(\dfrac{1}{2}\right)^6+2=\dfrac{\left(-3\right)^3}{4^3}-\dfrac{1^6}{2^6}+2\)

\(=\dfrac{-27}{\left(2^2\right)^3}-\dfrac{1}{2^6}+2=\dfrac{-27}{2^6}-\dfrac{1}{2^6}+2=\dfrac{-28}{2^6}+2\)

\(\dfrac{-28}{64}+2=\dfrac{-7}{16}+2=\dfrac{25}{16}\)

* \(-6,25+2,475-12,123=\dfrac{-250}{40}+\dfrac{99}{40}-12,123\)

\(=\dfrac{-250+99}{40}-12,123=\dfrac{-151}{40}-12,123=-3,775-12,123=-15,898\)