If 20 men can build a water fountain 56 metres long in 7 days, what length of a similar water fountain can be built by 35 men in 3 days?	Choose the correct answer:
A) 40 m B) 42 m C) 47 m D) 49 m E) 50 m

Rationale: "explanation : let the required length be x metres more men , more length built ( direct proportion ) less days , less length built ( direct proportion ) men 20 : 35 days 7 : 3 : : 56 : x therefore ( 20 x 7 x x ) = ( 35 x 3 x 56 ) x = ( 35 x 3 x 56 ) / 140 = 42 hence , the required length is 42 m . answer : b"
Answer: B