Hello!
Basically, we're going to take a value under X in chart A and plug it into equations in B and C. We're going to do this with all the values and if they always equal up to the Y value, it's proportional. I'll go through B.
y=4x-12.6
Let's plug in -2 for x.
y=(4)(-2)-12.6
y=-8-12.6
y=-20.6
-20.6 does NOT equal -10, therefore this equation is not proportional.