The problem gives us the following situation:
In this type of problem, we can use the theorem of conservation of energy. This tells us that the total energy on the system does not vary, although the for in which it is stored inside the system may vary. If we write the equation for this system we get:
On the first hill, our energy will be:
Thus, our energy on the system is 40859.565J. With this, we can find out how it is distributed in the second hill:
Then, we can isolate x:
Then, our height is x=10.829m