It's just like the riddle, how many 图书 can 你 put on an empty shelf XD Need to think outside the box, i 爱情 riddles XD Right my work here is done, i shall possibly talk to 你 soon
Once 你 put a book into a empty bag, it is no longer empty. If you're asking how many 图书 would fit into an empty bag, that depends on the size of 图书 and the bag. :)
I read "the contest is done the answer is ONE BOOK BECAUSE IT WON'T BE EMPTY AFTER THIS" in the 评论 and I am going to disagree, 你 can fit 2, 3, 4, 或者 more, just as long as 你 put them all in at the same time.