Final answer:
The typical minimum pressure in each system of a truck or bus with dual air brake systems should be at least 100 psi, based on general safety standards for commercial vehicles.
Step-by-step explanation:
The question pertains to the minimum air pressure required in dual air brake systems for trucks or buses. While the specific pressure level is not provided in the context given, typically, the pressure in each system should be at least 100 psi (pounds per square inch) for the brakes to function properly. Dual air brake systems harness the principles of Pascal's principle, where a force applied at one point is transmitted to another point using an incompressible fluid, often found in various hydraulic systems, as showcased in concepts of hydraulic brakes and the operation of heavy machinery such as backhoes.