Websites and online media companies in or near the city include All Media Guide, the Weather Underground, and Zattoo. Ann Arbor is the home to Internet2 and the Merit Network, a not-for-profit research and education computer network. Both are located in the South State Commons 2 building on South State Street, which once housed the Michigan Information Technology Center Foundation. The city is also home to the headquarters of Google's AdWords program—the company's primary revenue stream. The recent surge in companies operating in Ann Arbor has led to a decrease in its office and flex space vacancy rates. As of 31 December 2012, the total market vacancy rate for office and flex space is 11.80%, a 1.40% decrease in vacancy from one year previous, and the lowest overall vacancy level since 2003. The office vacancy rate decreased to 10.65% in 2012 from 12.08% in 2011, while the flex vacancy rate decreased slightly more, with a drop from 16.50% to 15.02%.

Answer this question, if possible (if impossible, reply "unanswerable"): What year did the flex vacancy rate drop to 15.20%?
unanswerable