Answer:
1. The car which is twice as massive as the other will have twice potential energy.
Step-by-step explanation:
The potential energy of an object is given by:

where
m is the mass of the object
g is the gravitational acceleration
h is the height of the object measured to some reference level
In this problem, we have two cars at same elevation (= same h in the formula) but one car has twice the mass of the second car. Calling m the mass of one car and 2m the mass of the second car, we have:
- Potential energy of the first car:

- potential energy of the second car:

So, the car which is twice as massive as the other will have twice potential energy.