You are given a math word problem and you are supposed to apply multiplication or division mathematical operators on the numbers embedded in the text to answer the following question and then only report the final numerical answer.

[EX Q]: Mrs. Hilt saw a rollercoaster . 7 students rode the rollercoaster every 5 minutes . How many students rode the rollercoaster in 15 minutes ?
[EX A]: 21

[EX Q]: A magician was selling magic card decks for 5 dollars each . If he started with 14 decks and by the end of the day he had 5 left , how much money did he earn ?
[EX A]: 45

[EX Q]: Chloe was organizing her book case making sure each of the shelves had exactly 6 books on it . If she had 5 shelves of mystery books and 4 shelves of picture books , how many books did she have total ?
[EX A]:
54