System of equations x+y = 7 3x-y=1

We can solve this system of equations by reduction method.
x+y=7
3x-y=1
-
4x=8    ⇒x=8/4=2
-3(x+y=7)
3x-y=1
-
-4y=-20  ⇒y=-20/-4=5
we can solve this systeme by susbtitution method.
x+y=7  ⇒ x=7-y
3x-y=1
3(7-y)-y=1
21-3y-y=1
-4y=1-21
-4y=-20
y=-20/-4=5
x=7-y=7-5=2