How to solve X + y = 2
X - y = 4

So y+x=2
x-y=4
one way is subsituteion where yousubisutte one of the number for another exg

x-y=4
add y to both sides
x=y+4
subsitute y+4 for x in x+y=2
 y+4+y=2
2y+4=2
subtract 4 from both sides
2y=-2
divide both sides by 2
y=-1
subsiutte
x+y=2
x-1=2
x=3

or elimination

x+y=2
x-y=4
add the two equations and cancel the y terms

x+x+y-y=2+4
2x=6
divide both sides by 2
x==3
subsitute
x+y=2
3+y=2
y=-1

so x=3
y=-1