The correct response is:
The acting president may retain office for a maximum of 10 years as long as there are more than two years left in the previous president’s term.
This is based on the 22nd Amendment to the U.S. Constitution, which limits a person to two elected terms as president, but allows for a vice president who has succeeded to the presidency to serve up to 10 years total if they take over with more than two years remaining in the term of the previous president.