Subject: mathqa
Question: arun and tarun can do a work in 10 days . after 4 days tarun went to his village . how many days are required to complete the remaining work by arun alone . arun can do the work alone in 20 days .
Option: 
A: 12 days .
B: 17 days .
C: 19 days .
D: 20 days .
Answer: A