Question

x-y=5
x+y=7 resposta

Answer 1

pela soma temos 
2x=12
x=6
se x=6
y=1 pois 6+y=7     ⇒y=7-6 ⇒y=1

Answer 2

x-y=5*(-1)

x+y=7

-x+y=-5

x+y=7

y=7-5

y=2

x+y=7

x+2=7

x=7-2

x=5