Final answer:
In a hydraulic brake system, one hydraulic system powers the inboard brakes and another hydraulic system powers the outboard brakes.
Step-by-step explanation:
In a hydraulic brake system, there are two hydraulic systems: one that powers the inboard brakes and another that powers the outboard brakes.
The inboard brakes are usually powered by the hydraulic system called 'hydraulic system #...' (the specific number is not provided in the question), while the outboard brakes are powered by the hydraulic system called 'hydraulic system #...' (the specific number is not provided in the question).