a: \(x-\dfrac{\left(-1\right)}{3}=2\dfrac{1}{4}\)
=>\(x+\dfrac{1}{3}=\dfrac{9}{4}\)
=>\(x=\dfrac{9}{4}-\dfrac{1}{3}=\dfrac{27-4}{12}=\dfrac{23}{12}\)
b: \(\dfrac{1}{3}+\dfrac{2}{3}:x=\dfrac{-4}{5}\)
=>\(\dfrac{2}{3}:x=-\dfrac{4}{5}-\dfrac{1}{3}=\dfrac{-12-5}{15}=-\dfrac{17}{15}\)
=>\(x=-\dfrac{2}{3}:\dfrac{17}{15}=-\dfrac{2}{3}\cdot\dfrac{15}{17}=-\dfrac{10}{17}\)
c: \(x:\dfrac{-2}{5}-\dfrac{3}{7}=\dfrac{-1}{3}\)
=>\(x:\dfrac{-2}{5}=\dfrac{3}{7}-\dfrac{1}{3}=\dfrac{2}{21}\)
=>\(x=\dfrac{2}{21}\cdot\dfrac{-2}{5}=-\dfrac{4}{105}\)