Solve for both systems 3x - y = 20 and x + y = 4

x + y = 4

x -x+ y = 4-x

y = 4-x

3x - y = 20

3x - (4-x) = 20

3x-4+x=20

4x-4=20

4x-4+4=20=4

4x=24

4x/4=24/4

x=6

y = 4-x

y = 4-6=-2