A and B can do a piece of work in 18 and 9 days respectively. A does the work for a few days and left, then B continued for 6 days. How many days did A and B work together?  Choose the correct choice from the following choices:
A) 1
B) 2
C) 3
D) 4
E) 5

Rationale: a and b work together for 2 days . a 1 day work 1 / 18 b 1 day work 1 / 9 let a work x days . then equation form is ( x / 18 ) + ( ( x + 6 ) / 9 ) = 1 from this equation x value is 2 . answer : b
Answer: B