Answer:
We have the system of equations:
y = -2*x
y = 2*x + 4.
To solve it by graphing, you need to graph both lines and see in which point the lines intersect each other.
You can see it in the image below. (blue is y = 2*x + 4, and green is y = -2*x)
We also can calculate the solution with math, let's do that:
y = -2*x
y = 2*x + 4.
We can replace the first equation in the second one, to get:
-2*x = 2*x + 4
Now let's solve this for x
-2*x -2*x = 4
-4*x = 4
x = 4/-4 = -1
Evaluating this in one of the equations we get:
y = -2*-1 = 2
Then the solution is the point (-1, 2), exactly what we can see in the graph.