`a, 1/3x + 2/5 + 2/3x = 4/9`
`⇒ x(1/3 + 2/3) + 2/5 = 4/9`
`⇒ x = 4/9 - 2/5`
`⇒ x = 2/45`
`b, 3|2x - 1| + 4 = 7`
`⇒ 3|2x - 1| = 3`
`⇒ |2x - 1| = 1`
`⇒` \(\left[ \begin{array}{l}2x-1=1\\2x-1=-1\end{array} \right.\)
`⇒` \(\left[ \begin{array}{l}2x=2\\2x=0\end{array} \right.\)
`⇒` \(\left[ \begin{array}{l}x=1\\x=0\end{array} \right.\)
`c, 2^(x + 2) + 2^x = 80`
`⇒ 2^x. 2^2 + 2^x = 80`
`⇒ 2^x.(4 + 1) = 80`
`⇒ 2^x. 5 = 80`
`⇒ 2^x = 16`
`⇒ 2^x = 2^4`
`⇒ x = 4`
