A can do a piece of work in 4 hours . A and C together can do it in just 2 hours, while B and C together need 3 hours to finish the same work. In how many hours B can complete the work ?  Choose the correct answer:
A) 10 hours
B) 12 hours
C) 16 hours
D) 18 hours
E) 20 hours

Rationale: "explanation : work done by a in 1 hour = 1 / 4 work done by b and c in 1 hour = 1 / 3 work done by a and c in 1 hour = 1 / 2 work done by a , b and c in 1 hour = ( 1 / 4 ) + ( 1 / 3 ) = 7 / 12 work done by b in 1 hour = ( 7 / 12 ) – ( 1 / 2 ) = 1 / 12 = > b alone can complete the work in 12 hour option b"
Answer: B