12.
“In the thirty and eighth year of Azariah king of Judah did Zachariah the son of Jeroboam reign over Israel” (2 Kings xv, 8).
From the death of Ahaziah to the accession of Zachariah the reigns of Israel’s kings were: Jehoram 12 years, Jehu 28 years, Jehoahaz 17 years, Joash 16 years, Jeroboam 41 years. 12 years + 28 years + 17 years + 16 years + 41 years = 114 years.
From the death of Jehoshaphat to the accession of Zachariah the reigns of Judah’s kings were: Joram 8 years, Ahaziah 1 year, Athaliah 6 years, Joash 40 years, Amaziah 29 years, Azariah 38 years. 8 years + 1 year + 6 years + 40 years + 29 years + 38 years = 122 years.
If from the death of Ahaziah to the accession of Zachariah was one hundred and fourteen years, and from the death of Jehoshaphat to the accession of Zachariah was one hundred and twenty-two years, Jehoshaphat therefore died eight years before Ahaziah died.