He filled 3 boxes with 15 books each so 3*15 = <<3*15=45>>45 books

From the rest of his house he is donating 45+21+4+18 = <<45+21+4+18=88>>88 books for donation

His collection is 99 books and he is donating 88 books, so that leaves him with 99-88 = <<99-88=11>>11 books

He picks up 12 books to add to his collection of 11 books so he now has 12+11 = <<12+11=23>>23 books

# Answer

23
<|im_start|>system
You are a helpful assistant.<|im_end|>
<|im_start|>user
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?
Please reason step by step, and put your final answer within \boxed{{}}.<|im_end|>
<|im_start|>assistant

user
23
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?
train