Answer:
intervene and tell the supervisor you had assumed responsibility for the paperwork and forgot
Explanation:
The golden rule is based on a principle of reciprocity and it states that one should treat others the way they want to be treated.
Different religions overtime have the same principle embedded in their doctrines.
In the given scenario where a coworker told you to compete some work for him before leaving and you failed to do so, when the coworker is being reprimanded you should take responsibility for the paperwork and say you forgot.
This is only fair on your coworker seeing it wasn't his fault the work was not done.
Also when you treat people fairly you can also be expected to be treated fairly too.