$A=(6-2\dfrac{4}{5})^3.\dfrac{1}{8}-1\dfrac{3}{5}:\dfrac{1}{4}$
$A=(6-\dfrac{14}{5})^3.\dfrac{1}{8}-\dfrac{8}{5}.4$
$A=(\dfrac{16}{5})^3.\dfrac{1}{8}-\dfrac{32}{5}$
$A=\dfrac{4096}{125}.\dfrac{1}{8}-\dfrac{32}{5}$
$A=\dfrac{512}{125}-\dfrac{32}{5}$
$A=\dfrac{512}{125}-\dfrac{800}{125}$
$A=\dfrac{-288}{125}$
$B=(\dfrac{-5}{4}-\dfrac{-3}{4}+\dfrac{7}{12}):20\%-\dfrac{1}{5}$
$B=(\dfrac{-15}{12}-\dfrac{-9}{12}+\dfrac{7}{12}):\dfrac{20}{100}-\dfrac{1}{5}$
$B=\dfrac{1}{12}.\dfrac{100}{20}-\dfrac{1}{5}$
$B=\dfrac{1}{12}.5-\dfrac{1}{5}$
$B=\dfrac{5}{12}-\dfrac{1}{5}$
$B=\dfrac{13}{60}$
