Final answer:
The potential difference VB - VA in the given scenario is calculated using the formula V=q/C, and with the values provided, the potential difference is determined to be 5 V.
Step-by-step explanation:
To calculate the potential difference VB - VA, we need to consider the given circuit elements: resistor R, capacitor C, supply voltage ε, charge q, and current I. Since specific details of the circuit, like configuration or the relationship between points A and B, are not given, we will demonstrate one of the possible ways to calculate the potential difference using the charge q on the capacitor and its capacitance C.
The potential difference across a capacitor can be found using the formula V = q/C, where V is the potential difference, q is the charge on the capacitor, and C is the capacitance. Using the given values, q = 20 mc (which should be read as 20 μC or 20 x 10-6 C) and C = 4.0 mF (which should be read as 4.0 μF or 4.0 x 10-6 F), the potential difference V = q/C = (20 x 10-6 C) / (4.0 x 10-6 F) = 5 V.
Therefore, the potential difference VB - VA across the capacitor is 5 V.