WASHINGTON (Reuters) - A financial package worth an estimated $51 million for Amazon.com Inc's second headquarters in northern Virginia was approved by the Arlington County Board on Saturday, helping the company clear a key hurdle amid protests. Amazon in November picked National Landing, a site jointly owned by Arlington County and the City of Alexandria, just outside Washington, along with New York City for its so-called HQ2 or second headquarters. The company has since scrapped its plans to build its headquarters in New York. (Reporting by Nandita Bose in Washington; Editing by Daniel Wallis)