Finding internal resistance of a battery?

Question

Question:

The following graph of potential difference versus current was obtained for a simple series circuit. Probe 1 is placed across a resistor, the slope of the line is 23.5 ohm and the y-intercept is 0.001 V. Probe 2 is placed across the battery in the circuit, the slope of the line is -2.03 ohm and the y-intercept is 2.45V. What is the internal resistance of the battery?

No graph is shown, so I'm thinking it's not really needed.

I tried using

I = E/R + r ...but am not really sure if thats in the right direction? I don't know how I would find the current? Any help would be greatly appreciated!

Answer 1

If the battery voltage drops at a rate of 2.03 volt per amp,  then 2.03 ohms is the internal resistance.