Question

What is the solution for the system of equations x+y=2 and x-y=4

Answer 1

X+y=2 (label equation one) 
x-y=4 (label equation two)

y=-x+2 (equation one rearranged, label this equation equation three)

sub 3 into 2
x-(-x+2)=4
x+x-2=4
2x-2=4
2x=6
x=3
sub x=3 into equation one

3+y=2
y=-1

therefore x=3 and y=-1