\(\dfrac{2}{5}\left(1-\dfrac{1}{2}x\right)-2=20\%\\ \dfrac{2}{5}\left(1-\dfrac{1}{2}x\right)-2=\dfrac{1}{5}\\ \dfrac{2}{5}\left(1-\dfrac{1}{2}x\right)=\dfrac{1}{5}+2\\ \dfrac{2}{5}\left(1-\dfrac{1}{2}x\right)=\dfrac{11}{5}\\ 1-\dfrac{1}{2}x=\dfrac{11}{5}\cdot\dfrac{5}{2}\\ 1-\dfrac{1}{2}x=\dfrac{11}{2}\\ \dfrac{1}{2}x=-\dfrac{9}{2}\\ x=-\dfrac{9}{2}\cdot2=x=-9\)