From the passage provided, extract the  population of Seattle metropolitan area

Context: Seattle is a seaport city on the West Coast of the United States. It is the seat of King County, Washington. With a 2020 population of 737,015, it is the largest city in both the state of Washington and the Pacific Northwest region of North America. The Seattle metropolitan area's population is 4.02 million, making it the 15th-largest in the United States. Its growth rate of 21.1% between 2010 and 2020 made it one of country's fastest-growing large cities.

Answer: The Seattle metropolitan area's population is 4.02 million, making it the 15th-largest in the United States