'Eighteenth' in the Bible

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

Now 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 was observed to the Lord in Jerusalem.