Need help with this!

[tdh10]

I need help figuring out how to solve this problem. Here goes...
Two sets of rollers feed a sheet of infinite length upwards. The rollers have to be opened periodically to prevent sheet bunching. The top rollers open every 'x' cycles for 1 cycle, same for the bottom rollers. Find the smallest number 'x' for both top and bottom so that both sets of rollers are never opened at the same time.
Thanks