we have
[tex]Az+17=-4z-b[/tex]
Adds the term [tex]4z[/tex] both sides
[tex]Az+17+4z=-4z-b+4z[/tex]
[tex]Az+17+4z=-b[/tex]
Subtract the term [tex]17[/tex] both sides
[tex]Az+17+4z-17=-b-17[/tex]
[tex]Az+4z=-b-17[/tex]
[tex]z(A+4)=-(b+17)[/tex]
Divide both sides by [tex](A+4)[/tex]
[tex]z=-(b+17)/(A+4)[/tex]
therefore
the answer is
[tex]z=-(b+17)/(A+4)[/tex]