'Eighteen' in the Bible

Jehoiachin was eighteen years old when he became king, and he reigned three months in Jerusalem; and his mother’s name was Nehushta the daughter of Elnathan of Jerusalem.

The height of the one pillar was eighteen cubits, and a bronze capital was on it; the height of the capital was three cubits, with a network and pomegranates on the capital all around, all of bronze. And the second pillar was like these with network.