What struck me from the first moment was the fact that computer X processes files TWICE as fast as computer Y. Use this to solve your problem in a matter of seconds. This means that while X processes 160 files, Y will process only 80 files. This means that the time you're looking for is the time it takes X to process 160 files.
240 files.............4 hours
160 files.............x hours

x = 160*4/240 = 16/6 = 2 hrs 4/6 = 2hrs and 40 mins.

Here is my take on it,

X produces 60 files per hour
Y Produces 30 files per hour

Working together they will produce 90 files per hour

90 files = 1 hour
240 files = 240 /90 hours = 2 hrs 40 min

Thank you. You guys are the best.......

I am getting there....one step a time..........

ST