How to solve y=-x+4; y=2x-8 using substitution?

In this problem why is the easiest to substitute.
Just set the equations equal to each other because they both equal y

-x + 4 = 2x - 8
(You want to get all the x's to one side so add x to each side)
4 = 3x - 8
(next add 8 to both sides)
12 = 3x
(lastly divide 3 from both sides)
4 = x
You have got your x so now it is time to find that y just replace x to either of the two equations
y = 2(4) -8   or  y = -(4) + 4
y = 8 - 8          y = 0
y = 0
Final  y=0, x=4