Since 2006, $9 billion has been invested in downtown and surrounding neighborhoods; $5.2 billion of that in has come in 20<answer>13</answer> and 2014. Construction activity, particularly rehabilitation of historic downtown buildings, has increased markedly. The number of vacant downtown buildings has dropped from nearly 50 to around <answer>13</answer>.[when?] Among the most notable redevelopment projects are the Book Cadillac Hotel and the Fort Shelby Hotel; the David Broderick Tower; and the David Whitney Building. Meanwhile, work is underway or set to begin on the historic, vacant Wurlitzer Building and Strathmore Hotel.[citation needed]
How many vacant downtown buildings are there in Detroit?
13