How do I figure out the dilution factor for this equation?

Long story short, I measured A280 of a protein with unknown concentration in mg/mL. I figured out the exact concentration doing a standard curve and regression line and yada yada yada. So that’s good.

But now, for the sake of seeing if this OTHER method still gives us the same numbers as what I did with the standard curves, I have to do the following equation to figure out the mg/mL concentration of the protein:

(absA280) (dilution factor)/Extinction coefficient of protein = concentration of protein

The extinction coefficient of this protein I’m working with is 51,300.

I’m just going to throw a random abs I got, so for example – .306.

The mg/mL I got using the standard curve equation is 2.52 mg/mL. Which is good. That was the 2.5 mg/mL standard.

But now that I’m using this equation, I can’t seem to get a number close to 2.52 mg/mL. I resorted to throwing numbers to plug in as the dilution factor as guesstimates, but I still got nothing remotely close.

So I really have no idea what they mean by “dilution factor” in terms of this equation. They don’t show an example, which is annoying.

NOTE: And yes – I tried solving for the dilution factor, treating it as X and I got some number that doesn’t make sense (like 422,47 blah blah)