I have tried my level best to understand this problem.Could anyone else please explain me how i solve this problem?

Note: I know Binary Indexed tree and want to solve this problem by this algorithm.Google search couldn't make a sense for myself to solve this problem.Everywhere,i saw,sort query according to it's value 'k'.And suggestion was that sort your given array also..But,i failed to get that!Pure explanation needed!

Thanks in advance!