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

[Q]: Megan was organizing her book case making sure each of the shelves had exactly 7 books on it . If she had 8 shelves of mystery books and 2 shelves of picture books , how many books did she have total ?
[A]: 70

[Q]: A person pays 145.8 dollars for 6 months use of an internet service . How much will 7 months of service cost ?
[A]: 170.1

[Q]: At lunch a waiter had 10 customers and 5 of them did n't leave a tip . If he got $ 3 each from the ones who did tip , how much money did he earn ?
[A]:
15