716/715 BC. This dating would be confirmed by the account of Hezekiah's illness in chapter 20, which immediately follows Sennacherib's departure (). This would date his illness to Hezekiah's 14th year, which is confirmed by Isaiah's statement () that he would live fifteen more years (29−15=14). These problems are all addressed by scholars who make reference to the ancient Near Eastern practice of coregency. Following the approach of Wellhausen, another set of calculations shows it is probable that Hezekiah did not ascend the throne before 722 BCE. By Albright's calculations, Jehu's initial year was 842 BC; and between it and Samaria's destruction the Books of Kings give the total number of the years the kings of Israel ruled as 143 7/12, while for the kings of Judah the number is 165. This discrepancy, amounting in the case of Judah to 45 years (165−120), has been accounted for in various ways; each of those positions must allow for Hezekiah's first six years to have fallen before 722 BCE. (However, Hezekiah beginning to reign before 722 BCE is consistent with a co-regency of Ahaz and Hezekiah from 729 BC.) Nor is it clearly known how old Hezekiah was when called to the throne; although states that he was twenty-five years of age, his father died at the age of thirty-six () and it is not likely that Ahaz had a son at the age of eleven. Hezekiah's son Manasseh ascended the throne twenty-nine years later, at the age of twelve. This places his birth in the seventeenth year of his father's reign, suggesting Hezekiah's age as forty-two, if he was twenty-five at his ascension. It is more probable that Ahaz was twenty-one or twenty-five when Hezekiah was born (suggesting an error in the text), and that the latter was thirty-two at the birth of his son and successor, Manasseh. Since Albright and Friedman, several scholars have explained these dating problems on the basis of a co-regency between Hezekiah and his father Ahaz between 729 and 716/715 BCE. Assyriologists and Egyptologists recognize that co-regency was practiced in both Assyria and Egypt. After noting that co-regencies were used sporadically in the northern kingdom (Israel), Nadav Na'aman writes, In the kingdom of Judah, on the other hand, the nomination of a co-regent was the common procedure, beginning from David who, before his death, elevated his son Solomon to the throne.... When taking into account the