Answer: 21 posters or 13 posters, please read the explanation since your wording was confusing.
Step-by-step explanation: Okay if you have two packs of 36 and 16 which is 104, you divide by 4 tacks. You end up getting 21 posters.
If you mean there are only 36 and 16 you get 52 and divide by 4. You end up having 13 posters.