I'm honestly confused about what you're trying to say. I'll give some generally information and you can tell me if it helped.

You're trying to use Beer's law, which relates absorbance to concentration using the equation:

A=ebc

-A =Absorbance

-e = Molar absorptivity

-b = Path length

-c = Concentration

You want to use a linear relationship (which I'll make apparent in a second) to find e, which works as a slope. When you're trying to use a graph to show a relationship, your basically taking a derivative of this equation (here comes some math). Basically, you're plotting the changes in A (dA, which you can't control so it's your independent or "y" axis) versus the change in concentration (dc, which you can control so it's your x). Therefor, if you look at your fun linear equation (y = mx + b), you can see that e (assuming pathlength is 1, or not a factor) is the slope. Once you measure the slope of the line, you can put in any concentration and get an absorbance and vice versa.

Does that help?

I'm not sure where your numbers are coming from since you're saying you "guessed"