12 persons can complete the work in 18 days. After working for 6 days, 4 more persons added to complete the work fast.In how many days they will complete the work?  Pick:
A) 10 B) 15 C) 17 D) 5 E) 9

Rationale: "total work = 12 * 18 = 216 units . after 6 days , work finished = 6 * 12 = 72 units . remaining units = 216 - 72 = 144 units . remaining days = 144 / ( 2 + 4 ) = 9 days the option is e"
Answer: E