A can do a piece of work in 4 hours; B and C together can do it in 2 hours, while A and C together can do it in 2 hours. How long will B alone take to do it? Choose the correct choice from the following:  A) 12  B) 9  C) 8  D) 6  E) 4

Rationale: "a ' s 1 hour ' s work = 1 / 4 ; ( b + c ) ' s 1 hour ' s work = 1 / 2 ; ( a + c ) ' s 1 hour ' s work = 1 / 2 . ( a + b + c ) ' s 1 hour ' s work = ( 1 / 4 + 1 / 2 ) = 3 / 4 . b ' s 1 hour ' s work = ( 3 / 4 - 1 / 2 ) = 1 / 4 . therefore a alone will take 4 hours to do the work . e"
Answer: E