`1-|(3x)/5 + 2/3| = 80%`
`⇔1-|(3x)/5 + 2/3| = 80/100=4/5`
`⇔|(3x)/5 + 2/3| =4/5-1`
`⇔|(3x)/5 + 2/3| =(-1)/5`
⇔\(\left[ \begin{array}{l}3x/5 + 2/3 =(-1)/5\\3x/5 + 2/3 =-(-1)/5\end{array} \right.\)
⇔\(\left[ \begin{array}{l}x=-13/9\\x=-7/9\end{array} \right.\)