$\dfrac{-5}{12}$+$\dfrac{7}{12}$.$\dfrac{8}{13}$+$\dfrac{7}{12}$.$\dfrac{5}{13}$
=$\dfrac{-5}{12}$+$\dfrac{7}{12}$.($\dfrac{8}{13}$+$\dfrac{5}{13}$)
=$\dfrac{-5}{12}$+$\dfrac{7}{12}$.$\dfrac{13}{13}$
=$\dfrac{-5}{12}$+$\dfrac{7}{12}$.`1`
=$\dfrac{-5}{12}$+$\dfrac{7}{12}$
=$\dfrac{2}{12}$
=$\dfrac{1}{6}$