we have
[tex](3x+2)^{2}+7(3x+2)-8=0[/tex] --------> equation [tex]1[/tex]
let's change of variable
[tex]u=(3x+2)[/tex] --------> equation [tex]2[/tex]
substitute in the equation [tex]2[/tex] in equation [tex]1[/tex]
[tex](u)^{2}+7(u)-8=0[/tex]
therefore
the answer is
[tex](u)^{2}+7(u)-8=0[/tex]
