'Eighteen' in the Bible

Or those eighteen, on whom the tower in Siloam fell, and killed them; do you think that they were worse offenders than all the men who dwell in Jerusalem?

Behold, there was a woman who had a spirit of infirmity eighteen years, and she was bent over, and could in no way straighten herself up.

Ought not this woman, being a daughter of Abraham, whom Satan had bound eighteen long years, be freed from this bondage on the Sabbath day?"