Answer:
He could release the brakes.
Explanation:
Gravitational potential energy is energy stored in an object due to its position, or height.
When Mr. Phillips' car is at the top of the hill, it has gravitational potential energy because it has the potential to roll down the hill. If the car started rolling down the hill, this potential energy would be transformed into kinetic energy. The easiest way to do this is to release the brakes.
Starting the engine or pushing the car up the hill would also be types of energy transformations, but they would not be transforming the gravitational potential energy into kinetic energy.
