a, \(\frac{-2}{5x}\) +\(\frac{1}{5}\) =\(\frac{3}{10}\)
⇒\(\frac{-4}{10x}\) +\(\frac{2x}{10x}\) =\(\frac{3x}{10x}\)
⇒-4 +2x=3x
⇒x=-4
b, 0,5x-\(\frac{2}{3}\)=\(\frac{7}{12}\)
⇒\(\frac{x}{2}\) -\(\frac{2}{3}\)=\(\frac{7}{12}\)
⇒\(\frac{6x}{12}\) -\(\frac{8}{12}\) =\(\frac{7}{12}\)
⇒6x-8=7
⇒6x=15
⇒x=\(\frac{15}{6}\)