Hello! I'm guessing you're studying circuit diagrams or of the like? I'm actually in grade 11 and just finished this unit!
In any case, you can use Ohm's law, V=IR and it's rearranged forms, to solve problems like these!
In regards to potential difference, you are solving for V... Where I is the current (in amps) and R is the resistance (in ohms).
If I was to say, determine the potential difference over a resistor of 12ohms with a current flow of 2A.
You would sub in the known values and solve:
Therefore, the potential difference is 24 volts!
Hope this helps! :)