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?

这道题怎么算啊·~各位大侠帮帮忙吧！！最怕这种涉及效率的题目了