Question

x + y = 8
x - y = 4

Answer 1

x+y=8
x-y=4

x-x+y-(-y)=8-4
2y=4
y=4/2
y=2

x-y=4
x-(2)=4
x-2=4
x=4+2
x=6

Answer 2

x + y   = 8
x -  y   = 4
_________
2x        = 12
x= 12/2
x = 6

6+ y =8
y = -6 + 8
y = 2