Resposta:
12
Explicação passo a passo:
+3x-4= 12
[tex]3x-4=y\\\\3x-y-4=0\\\\(3) \ . \ x+(-y-4)=0\\\\x=\frac{-(-y-4)}{3} \\\\x=\frac{1}{3} y+\frac{4}{3}[/tex]
