Your answer, "42", is not correct.
The correct answer to
How old was Ahaziah when he began to reign?
is
22
as shown by
2 Kings 8:26
which is
- KJV
- Two and twenty years old was Ahaziah when he began to reign; and he reigned one year in Jerusalem. And his mother's name was Athaliah, the daughter of Omri king of Israel.
- NIV
- Ahaziah was twenty-two years old when he became king, and he reigned in Jerusalem one year. His mother's name was Athaliah, a granddaughter of Omri king of Israel.