6.
“And Joram [Jehoram] king of Israel and Ahaziah king of Judah went out, each in his chariot ... against Jehu” (2 Kings ix, 21), “And Jehu drew a bow with his full strength, and smote Jehoram between his arms, and the arrow went out at his heart” (24). “But when Ahaziah the king of Judah saw this he fled by way of the garden house. And Jehu followed after him, and said, Smite him also in the chariot. And they did so” (27).
Jehoram, king of Israel, and Ahaziah, king of Judah, were thus slain at the same time. Jehu succeeded Jehoram; Athaliah succeeded Ahaziah, reigned six years, and was in turn succeeded by Joash. Jehu had thus reigned six years over Israel when Joash became king of Judah. As Jehoram reigned twelve years, from the death of Ahaziah [of Israel] to the accession of Joash then, was eighteen years.
From the death of Jehoshaphat to the accession of Joash, Judah’s sovereigns reigned as follows: Joram 8 years, Ahaziah 1 year, Athaliah 6 years—a total of fifteen years.
If from the death of Ahaziah to the reign of Joash was eighteen years, and from the death of Jehoshaphat to the reign of Joash was fifteen years, Jehoshaphat therefore died three years after Ahaziah died.