a:\(=5-\dfrac{7}{39}\cdot\dfrac{13}{7}+\dfrac{2}{9}=5-1+\dfrac{2}{9}=4+\dfrac{2}{9}=\dfrac{38}{9}\)
b: \(=\dfrac{28}{15}:\dfrac{3}{4}-\left(\dfrac{11}{20}+\dfrac{5}{20}\right)\cdot\dfrac{3}{7}\)
\(=\dfrac{112}{45}-\dfrac{4}{5}\cdot\dfrac{3}{7}\)
\(=\dfrac{112}{45}-\dfrac{12}{35}=\dfrac{676}{315}\)