'Year of' in the Bible

In the month Nisan in the twentieth year of king Artaxerxes, when the wine stood before him, I took up the wine, and gave it unto the king and I was heavy in his presence.

And from the time forth that it was committed unto me to be a captain in the land of Judah, namely from the twentieth year even unto the two and thirtieth year of king Artaxerxes - that is twelve years - I and my brethren lived not of such sustenance as was given to a captain:

But in all this was not I at Jerusalem: for in the two and thirtieth year of Artaxerxes king of Babylon, came I unto the king, and after certain days obtained I license of the king