Reconstruct a question, answer pair from this explanation: He sold an average of 16 books per month across all 3 months so he must have sold a total of 3 * 16 = 48 books in those 3 months. He sold 15 + 16 = 31 in January and February. He must have sold 48 - 31 = 17 books in March.
Q:A bookseller sells 15 books in January, 16 in February and a certain number of books in March. If the average number of books he sold per month across all three months is 16, how many books did he sell in March?
A:17