Give the step-by-step reasoning process and then the final answer. Henry needs to declutter his book collection of 99 books. From his bookshelf, he was able to fill 3 boxes of 15 books each to take to a donation center. He had 21 books in a room he could donate, 4 on his coffee table and 18 cookbooks stashed in the kitchen. When he dropped them off, he noticed a box of books that had a "free to a good home" note. He grabbed 12 books to take back to his place. How many books does Henry now have?
He filled 3 boxes with 15 books each so 3 * 15 = 45 books. From the rest of his house he is donating 45 + 21 + 4 + 18 = 88 books for donation. His collection is 99 books and he is donating 88 books, so that leaves him with 99 - 88 = 11 books. He picks up 12 books to add to his collection of 11 books so he now has 12 + 11 = 23 books.
The final answer: 23.