A manufacturer packages its product in cylindrical containers

A manufacturer packages its product in cylindrical containers. The cylinders are then placed in rectangular boxes for shipping. Assuming there are no constraints on the dimensions of the rectangular boxes, what is the approximate minimum amount of unoccupied space in each box?

The answer I am getting is 22%, but given answer is 15%. Can anyone explain why?

The answer should be 22%, and hence there is a bug. I have flagged this question.

The bug has been fixed.