Which sentence contains correct punctuation? they spent three days’ vacation building terraces and landscaping the yard! they spent three days vacation building terraces and landscaping the yard! they spent three day’s vacation building terraces and landscaping the yard!

They spent three days’ vacation building terraces and landscaping the yard!

Explanation:

The sentence "they spent three days’ vacation building terraces and landscaping the yard!" has a possessive plural noun. When there is a plural noun that ends with a final "s" the apostrophe must be placed after the "s" of the plural noun. It is not correct to say "They spent three day's vacation" because It is not a day or one day in its singular form. It's been three days.