At a loading dock, each worker on the night crew loaded 3/4 as many boxes as each worker on the day crew. If the night crew has 4/7 as many workers as the day crew, what fraction of all the boxes loaded by the two crews did the day crew load?  Choose the correct choice from the following.
A) 7 / 10 B) 2 / 5 C) 3 / 5 D) 4 / 5 E) 5 / 8

Rationale: "method : x = no . of boxes loaded by day crew . boxes by night crew = 3 / 4 * 4 / 7 x = 3 / 7 x % loaded by day crew = x / ( x + 3 / 7 x ) = 7 / 10 answer a"
Answer: A