\(a,=\dfrac{2.6-4.10-15}{30}\\ =-\dfrac{43}{30}\\ b,B=\dfrac{1}{3}-\left[\left(-\dfrac{5}{4}\right)-\left(\dfrac{2+3}{8}\right)\right]\\ =\dfrac{1}{3}-\left(-\dfrac{5}{4}-\dfrac{5}{8}\right)\\ =\dfrac{1}{3}-\left(\dfrac{-5.2-5}{8}\right)\\ =\dfrac{1}{3}+\dfrac{15}{8}\\ =\dfrac{8+15.3}{24}\\ =\dfrac{53}{24}\)
