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.
Q: Question: A can finish a piece of work in 5 days. B can do it in 15 days. They work together for two days and then A goes away. In how many days will B finish the work?

 Option A: 3 days

 Option B: 5 days

 Option C: 4 days

 Option D: 6 days

 Option E: 7 days
A: 
Option E