'Eighteenth' in the Bible

Now Joram the son of Ahab had become king over Israel in Samaria in the eighteenth year of Jehoshaphat king of Judah. He reigned twelve years

It happened in the eighteenth year of King Josiah, the king sent [word to] Shaphan the son of Azaliah the son of Meshullam, the secretary of the temple of Yahweh, saying,

But in the eighteenth year of King Josiah, this Passover was kept for Yahweh in Jerusalem.