'Eighteenth' in the Bible

And Jehoram, the son of Ahab, became king over Israel in Samaria in the eighteenth year of the rule of Jehoshaphat, king of Judah; and he was king for twelve years.

Now in the eighteenth year after he became king, Josiah sent Shaphan, the son of Azaliah, the son of Meshullam, the scribe, to the house of the Lord, saying to him,

In the eighteenth year of the rule of King Josiah this Passover was kept to the Lord in Jerusalem.