Although the question is incomplete, I have seen it before.
The equations are:
3a + 6b = 12
-3a + 6b = -12
Adding the equations, we get:
12b = 0
And b = 0
I'm not totally sure the exact answer, or if this even helps, but the Y intercept is changing from -2 to 5
Each piece will be 6 inches, and there will be 7 I believe.
Substitue what y equals for y and solve.

Hope this helps.