The 3D picture above is a representation of the room as I’ve interpreted it. It can be viewed through coloured filters (green or blue for the right eye and red for the left eye). The line AFG is the pole with cables attached to point F from each corner of the room. F is 8ft below the top of the pole A. The floor diagonals are shown as dotted lines. The numbers on the axes represent feet.
Assuming the cables are attached to the four corners of the floor, they form 4 right triangles with common leg FG: DFG, EFG, BFG, CFG. These triangles are congruent. The base leg has length=√(30²+40²)=50. FG=25-8=17 feet. Each cable has length=√(50²+17²)=√(2500+289)=√2789=52.81 feet.