By July 2007, the Shadow platform accumulated 200,000 flight hours, doubling its previous record of 100,000 hours in 13 months. The system then surpassed 300,000 flight hours in April 2008, and by May 2010, the Shadow system had accumulated over 500,000 flight hours. As of 2011, the Shadow had logged over 709,000 hours. The Shadow platform has flown over 37,000 sorties in support of operations in Iraq and Afghanistan by US Army and Army National Guard units. On 6 August 2012, AAI announced that the Shadow had achieved 750,000 flight hours during more than 173,000 missions. More than 900,000 flight hours had been logged by Shadow UAVs by the end of June 2014.
Question: How many years did it take the Shadow to go from 300000 hours to 500000 hours?
Answer: 2