GWD数学题请教

melody远行

Running at their respective constant rates, machine X takes 2 days longer to produce w widgets than machine Y.At these rates, if the two machines together produce 5/4 w widgets in 3 days, how many days would it take machine X alone to produce 2w widgets?

A.4
B.6
C.8
D.10
E.12
这题算了好久没算正确，有同学能教一下吗？感谢！答案是E

easttiger2010

X_rate= a；
Y_rate= b

1） w/a=w/b+2
2)   a+b=(5w/4)/3

a= w/6 or 5w/4 (>5w/12, 排除)

3) 2w/(w/6)= 12