You are given a math word problem and you are supposed to make use of mathematical concepts like probability, combinatorics, linear equations, sequences/series, or simple operators like addition, subtraction, division, or multiplication to answer the given question. Choose the best option from the 5 given options and report that option.

[EX Q]: Question: A and B complete a job in 6 days. A alone can do the job in 15 days. If B works alone, how many days will it take to complete the job?

 Option A: 8

 Option B: 10

 Option C: 12

 Option D: 14

 Option E: 16
[EX A]: Option B

[EX Q]: Question: Two dice are tossed. The probability that the total score is a prime number is:

 Option A: 5/5

 Option B: 5/9

 Option C: 5/1

 Option D: 5/7

 Option E: 5/12
[EX A]: Option E

[EX Q]: Question: A cyclist bikes x distance at 8 miles per hour and returns over the same path at 10 miles per hour. What is the cyclist's average rate for the round trip in miles per hour?

 Option A: 8.1

 Option B: 8.9

 Option C: 8.6

 Option D: 8.3

 Option E: 9
[EX A]:
Option B