a)
\(x+\dfrac{1}{3}=\dfrac{7}{26}\\ x=\dfrac{7}{26}-\dfrac{1}{3}=\dfrac{21}{78}-\dfrac{26}{78}=-\dfrac{5}{78}\)
b)
\(\dfrac{x}{150}=\dfrac{5}{6}\cdot\dfrac{-7}{25}\\ \dfrac{x}{150}=\dfrac{-7}{30}\\ x\cdot30=-150\cdot7\\ x=\dfrac{-150\cdot7}{30}=-35\)