'Eighteenth' in the Bible

Jehoram the son of Ahab became king over Israel in Samaria in the eighteenth year of Jehoshaphat king of Judah, and reigned twelve years.

In the eighteenth year of King Josiah, the king sent Shaphan the son of Azaliah, the son of Meshullam the scribe to the house of the Lord, saying,

But in the eighteenth year of King Josiah, this Passover to the Lord was kept in Jerusalem.