A can do a piece of work in 5 hours; B and C together can do it in 3 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 choices:
A) 30  B) 20  C) 10  D) 6  E) 5
A's 1 hour's work = 1/5 ;   (B + C)'s 1 hour's work = 1/3 ;   (A + C)'s 1 hour's work = 1/2 .   (A + B + C)'s 1 hour's work = ( 1/5 + 1/3 ) =8/15 .   B's 1 hour's work = ( 8/15 - 1/2 ) = 1/30.   Therefore A alone will take 30 hours to do the work.   30
<result>A</result>
A can do a piece of work in 5 hours; B and C together can do it in 3 hours, while A and C together can do it in 2 hours. How long will B alone take to do it?