Physics--How to determine potential difference

Here's the problem:

In a series circuit, if the potential difference across the battery is 20 V and the potential difference across R1 is 12 V, what is the potential difference across R2?

I know that in a series circuit, the current is the same through all of the resistors. Does that mean that the potential difference is the same everywhere too, or no? If not then how can I find it?

Thank you! : )

the total voltage drop must equal the total voltage increase due to conservation of energy, so 8V