Final answer:
If a single fracture involves both the skull vault and base, and both are equal in severity, both skull vault and base fractures should be coded.
Step-by-step explanation:
If a single fracture involves both the skull vault and base, and both are equal in severity, the correct code to assign would be 3) Both skull vault and base fractures. This is because when both the skull vault and base are affected in a fracture, both need to be coded. It is important to accurately capture the location and extent of the injury when assigning codes for fractures.