Force Required to Lift Door

I have a relatively simple mechanics problem that I am stuck on at work. I need to calculate the force required to lift a bifold door using lift cables.

Background:

Bifold doors are a type of door where the top of the top section is hinged to the header and the bottom is hinged to the bottom half of the door. Lift straps or cables are used to pull the bottom of the door upwards. There are rollers on the bottom of the door that roll up the side of the building as the door opens. I have included a picture pulled from Pinterest for use as a visual reference.

thnx!

I didn’t find the right solution from the Internet.
References: http://www.engineersedge.com/engineering-forum/showthread.php/4894-Force-Required-to-Lift-Door?s=faa01278f2f992dee52194536fa5ccf3

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