Respostas

2014-08-18T09:49:34-03:00
X+y=20
x-y+30

x = 30+y

x+y=20
30+y+y=20
2y=20-30
2y=-10
y = -10/2
y = -5

x+y=20
x-5=20
x=20+5
x=25