Respostas

2013-12-11T18:45:05-02:00
X+y=20➡️y=20-x
2x+4y=20
2x+4.(20-x)=20
2x+80-4x=20
2x-4x=20-80
-2x=-60
X=-30
y=20+30
y=50
havia 30 patos e 50 porcos