Answer:
Both forces are the same.
Explanation:
The problem states that:

The force exerted on the moon by earth is given by:
where K is the gravitational constant, and d is the separation distance between the earth and the moon.
The force exerted on the earth by moon is given by:
where K is the gravitational constant, and d is the separation distance between the earth and the moon.
The relation is therefore:

As you can see, they are the same.
Answer:
Stunt Car A experiences a large force over a short period of time. Stunt Car B experiences a small force over a long period of time. Because of the force experienced by Stunt Car A, it will sustain more damage than Stunt Car B.
Explanation:
Both cars have the same mass and velocity, therefore they have the same momentum. During the collision, the total momentum of the car A and brick wall is conserved as well as the total momentum of the car B and the pile of leaves.
However, if we are to investigate the damage on each car, we should look at the cars not the whole system. So, the momentum difference between the cars gives us the impulse that the car felt.

Since the Car A will crash the wall quicker than the other car crashes through the pile of leaves,

which gives us