\(\left(6-2\dfrac{4}{5}\right).3\dfrac{1}{8}-1\dfrac{3}{5}:\dfrac{1}{4}\)
\(=\left(6-\dfrac{14}{5}\right).\dfrac{25}{8}-\dfrac{8}{5}:\dfrac{1}{4}\)
\(=\dfrac{16}{5}.\dfrac{25}{8}-\dfrac{8}{5}:\dfrac{1}{4}\)
\(=10-\dfrac{8}{5}.4\)
\(=10-\dfrac{32}{5}\)
\(=\dfrac{18}{5}\)