(a) How many buildings does his department own, (b) in each case, how many of these buildings have been vacant for longer than six months and (c) what amount has his department spent on the maintenance of all its vacant buildings (i) in the (aa) 2011-12, (bb) 2012-13 and (cc) 2013-14 financial years and (ii) from 1 April 2014 up to the latest specified date for which information is available?