'Eighteenth' in the Bible

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

And it came to pass in the eighteenth year of king Josiah, that the king sent Shaphan, the son of Azaliah the son of Meshullam, the scribe, to the house of Jehovah, saying,

but in the eighteenth year of king Josiah was this passover kept to Jehovah in Jerusalem.