A can do a piece of work in 10 days. He works at it for 4 days and then B finishes it in 9 days. In how many days can A and B together finish the work?  Choose the correct choice from the following answers:
A) 6
B) 8
C) 12
D) 15
E) 20
4/10+9/X = 1/x = 15   1/10+1/15 = 1/6 = 6 days   6NSWER 6
<result>A</result>
A can do a piece of work in 10 days. He works at it for 4 days and then B finishes it in 9 days. In how many days can A and B together finish the work?