Resposta :
Então, é só substituir. Onde tem "y" colocamos a equação equivalente "2x-5":
[tex]3x+2y=4 \\\\ 3x + 2 \cdot (2x-5) = 4 \\\\ 3x+(2 \cdot 2x) + (2 \cdot -5) = 4 \\\\ 3x+4x-10 = 4 \\\\ 7x = 4+10 \\\\ 7x = 14 \\\\ x =\frac{14}{7} \\\\ \boxed{\boxed{x = 2}}[/tex]
[tex]3x+2y=4 \\\\ 3x + 2 \cdot (2x-5) = 4 \\\\ 3x+(2 \cdot 2x) + (2 \cdot -5) = 4 \\\\ 3x+4x-10 = 4 \\\\ 7x = 4+10 \\\\ 7x = 14 \\\\ x =\frac{14}{7} \\\\ \boxed{\boxed{x = 2}}[/tex]