Respostas

2014-05-17T15:00:07-03:00
2x+y=80y
2x=80y-y
2x=80
x=80÷2
x=40
80y=x+20
80y=40+20
80y=60
y=60÷80
y=0,75
2014-05-17T15:06:48-03:00
2x+y=80 e y=x+20
Substitui os valores:
2x+x+20=80
3x=80-20
x=60÷3
x=20