While the repair shop works on your voltmeter, they loan you an unusual replacement: Rather than measuring the potential difference across a resistor, it measures the amount of charge that flowed, and the change in electric potential energy of that charge. You use the device on a resistor and it tells you that 2.5 C of charge flowed through it, and that the electric potential energy of that charge decreased by 0.40 J. What is the potential difference across the resistor? (Report the answer as a positive number.)