After working for 6 days, David was joined by Moore. Together they completed the remaining job in 3 days. How many days will it take both of them to complete the entire job, given that it would have taken David 12 days to complete the job alone? Select the correct option
A) 7  B) 4  C) 6  D) 2  E) 7

Rationale: explanation : david and moore complete half work in 3 days = > they can complete whole work in 6 days answer : option c
Answer: C