Not clear how to add bounties for questions such as these. On my view of this question there's no start a bounty button. Any help appreciated.
A bounty can be started on a question two days after the question was asked.
The question you want to award a bounty for was posted on 2015-08-22 at 20:45:40Z, now it's 2015-08-24 at 13:41Z. You'll be able to start a bounty in 7 hours.
There is no requirement for the question to be unanswered (one bounty reason is "to reward an existing answer").
According to FAQ about bounty:
If you’ve asked a good question, edited it with status and progress updates, and still are not receiving answers, you can draw attention to your question by placing a bounty on it.
The question linked have already received an accepted answer. So you shouldn't be enable to give one.