\(a,\dfrac{15}{28}+\dfrac{-1}{4}=\dfrac{15}{28}+\dfrac{-7}{28}=\dfrac{8}{28}=\dfrac{2}{7}\\ b,\dfrac{2}{7}-\dfrac{-1}{4}=\dfrac{8}{28}-\dfrac{-7}{28}=\dfrac{15}{28}\)
\(c,\dfrac{-14}{3}:2=\dfrac{-14}{3}\times\dfrac{1}{2}=\dfrac{-7}{3}\\ d,\dfrac{-7}{15}.\dfrac{5}{8}.\dfrac{15}{-7}.\left(-16\right)=\left(\dfrac{-7}{15}.\dfrac{15}{-7}\right)\left[\dfrac{5}{8}.\left(-16\right)\right]=1.\left(-10\right)=-10\)