'Year of' in the Bible

The words of Nehemiah son of Hacaliah:Now it happened in the month of Chislev, in the twentieth year [of the Persian king], as I was in the capitol of Susa,

In the month of Nisan, in the twentieth year of King Artaxerxes, when wine was placed before him, I took the wine and gave it to the king. Now I had not [previously] been sad in his presence.

Moreover, from the day that I was appointed to be their governor in the land of Judah, from the twentieth year to the thirty-second year of King Artaxerxes, for twelve years, neither I nor my relatives have eaten the governor’s food allowance.

But during all this time I was not at Jerusalem, for in the thirty-second year of Artaxerxes [Persian] king of Babylon I went to the king. Then after some time I asked for a leave [of absence] from the king,