\(A=\dfrac{1}{7}\left(\dfrac{3}{8}+\dfrac{5}{8}\right)+\dfrac{-1}{7}=\dfrac{1}{7}-\dfrac{1}{7}=0\)
\(B=\dfrac{4}{9}\cdot\dfrac{5}{13}+\dfrac{4}{9}\cdot\dfrac{8}{13}-\dfrac{1}{2}=\dfrac{4}{9}-\dfrac{1}{2}=\dfrac{8-9}{18}=\dfrac{-1}{18}\)
\(C=\left(\dfrac{2}{3}\right)^{22}\cdot\left(\dfrac{2}{3}\right)^{12}:\left(\dfrac{2}{3}\right)^{30}=\left(\dfrac{2}{3}\right)^4\)