Final answer:
A guard rail system or personal fall arrest system is required on scaffolds over 10 feet high. The provided numerical question involves calculating cable tensions and is separate from the safety requirement.
Step-by-step explanation:
A guard rail system or a personal fall arrest system is required on scaffolds more than 10 feet (3 meters) above a lower level to prevent falls and provide safety to individuals working on the scaffold. The question provided seems to be a mix of a standard safety requirement and a specific physics problem related to forces acting on a scaffold. While the safety regulation is straightforward, solving the physics problem involves understanding the principles of static equilibrium and calculating the tension in the scaffold-supporting cables.