Subject: mathqa
Question: a can do a piece of work in 90 days & y can do it in 80 days . they began working together but a leaves after some days and then b completed the remaining work in 46 days . the number of days after which a left the work was ?
Option: 
A: 18 days
B: 16 days
C: 12 days
D: 21 days
Answer: B