Q: WHAT YEAR DID JEHOSHAPHAT BEGIN HIS REIGN IN JUDAH?
A: IT DEPENDS WHAT CALENDAR YOU ARE USING!
On the Gregorian calendar (the one you might have on your wall) the year was 855 BC.
On the Hebrew calendar, sometimes called the biblical calendar, the year was 3192 AM.
I Kings 22:41-42 – And Jehoshaphat the son of Asa began to reign over Judah in the fourth year of Ahab king of Israel. Jehoshaphat was thirty and five years old when he began to reign; and he reigned twenty and five years in Jerusalem. And his mother's name was Azubah the daughter of Shilhi.