\(a,\dfrac{3}{8}\times\dfrac{2}{5}:\dfrac{3}{4}\)
\(=\dfrac{3}{8}\times\dfrac{2}{5}\times\dfrac{4}{3}\)
\(=\dfrac{3\times2\times4}{8\times5\times3}\)
\(=\dfrac{1\times1\times1}{1\times5\times1}\)
\(=\dfrac{1}{5}\)
\(b,\dfrac{5}{3}+9-\dfrac{3}{8}\)
\(=\dfrac{32}{3}-\dfrac{3}{8}\)
\(=\dfrac{256}{24}-\dfrac{9}{24}\)
\(=\dfrac{247}{24}\)