Question

x + y = 28 / x - y = 12 .. me ajudem

Answer 1

$\left \{ {{x+y=28} \atop {x-y=12}} \right.$

isolando o x:  x = 12 + y

Substituindo:  12 + y + y = 28 >> y = 8

Decobrindo x agora:  8 + x = 28 >> x = 20

Answer 2

X+Y=28
X-Y=12
X=16 e Y=12