247. When did Jehoash become king of Israel?

At least forty years after Joash became king of Judah.

In the three and twentieth year of Joash the son of Ahaziah king of Judah Jehoahaz the son of Jehu began to reign over Israel in Samaria, and reigned seventeen years. 2 Kings 13:1

In the thirty seventh year of Joash's reign.

In the thirty and seventh year of Joash king of Judah began Jehoash the son of Jehoahaz to reign over Israel in Samaria. 2 Kings 13:10