Question

resolva o sistema

x+y=4
3x+y=28

Answer 1

y = 4-x

3x +4-x = 28

2x= 24
x=12

Answer 2

Vamos lá...

x+y=4

3x+y=28

1==>y+x =4

2==>y+3x = 28

2==> y= -3x+28

         x+(-3x+28)=4

        -2x = - 24 (-1)

         2x = 24

          x = 24/2

          x=12

y= -3x+ 28

y=-3(12) + 28

y =-36+24

y=-8

Bons estudos.